Autoconverted maps and map difficulty:
While autoconversion is better than I expected it to be, it still rarely presents the player with any of the same mapping structures that you would see in proper mania maps. They can be good practice, but often times even in relatively easy autoconversions, players can be presented with more difficult patterns (odd chords one after the other, holds+notes on otherwise easy maps, etc.). When playing easier maps and learning the game, players should be presented with a progression of skill. What I mean by this is that for the easiest maps, you shouldn't ever have 3 note chords one after the other, especially not something like 124 then 347, nor should you present them with holds+notes, or quick triplets, chord holds, holds starting at different times, or structures like this: 1, 1, 13, 1, 3. Those things should be gradually introduced to players. However, this should absolutely not force a mapper to leave every slightly difficult pattern out of an easier map. They should pick and chose 1 or 2 of those features that would be more appropriate for how the song is, and use them sparingly. (EDIT to clarify, the numbers I use here for patterns are column numbers. 2 numbers beside each other means a chord, the commas separate the notes/chords, these numbers are based on 7k, but the idea applies to all key numbers).
There is something that plagues osu standard that I really hope does not carry over into mania as far as actual difficulty spread. In standard the difficulty spread is generally more or less the same for every single map, despite the fact that some songs would benefit from a much higher overall difficulty. If you look at maps in o2jam, there were some who's difficulty levels ranged from say 1 to 10 between 3 difficulties, and yet there were also some maps where the easiest difficulty might be a 15, and the hardest a 60, with the medium somewhere between them. I would much prefer this approach as it gives the mapper more room to work with how exactly their map feels at every difficulty. I'm not suggesting that mappers should be allowed to make an "easy" as hard as a standard hard (although I wouldn't be opposed to allow that in approved maps), but I think more lenience on that should be allowed. If you want to map something like xepher, and make it like a "boss map" designed specifically to be legitimately harder than similar difficulty levels of other maps, it should be allowed. To reiterate, standard osu feels too "samey" between maps. Most hards are within a rather small range of difficulty, etc. Maybe coming up with a better difficulty rating would be necessary if something like this were implemented, but the lack of a more accurate difficulty rating system shouldn't stop something like that from being considered.
The "sliding difficulty window" in o2jam created a sense of progression that osu doesn't have. You could clearly see if a song had an easy that was a 15, or even higher, that song was hard period, and only got harder from there. It allowed a song to be characterized as a harder or easier song overall. It meant that the really easy songs could have 3 difficulties all in the 1-5 range if they wanted and the harder songs could have a range from say 20-50, or whatever. Each song could be placed as roughly easier or harder than some other songs, and as you got better you kinda felt like you were really moving up from "easier songs" to "harder songs". It also meant that as you were learning on the easier songs, once you got too good to play the easy difficulty on a song, you didn't always have a large jump on that song between easy and medium, sometimes by the time you got too good for the easy, you were at the right level for the medium. In short: moving between difficulties in osu usually involves some considerable jump in difficulty, and this system directly works against that since a medium might be a very easy medium (just slightly harder than an easy) or a very hard medium (possibly harder than even a hard on easier songs). (this only works well provided that you have a good sense of pattern difficulty progression as I mentioned earlier between easy medium, and hard maps.)
Use of rules and guidelines:
I agree with Silynn that rules and guidelines should be relaxed. We have a system that pushes for extensive community modding, we should make good use of it.
People have been mapping for mania style (whether 4, 6, or 7k) for years now in various different games, none of which have anything remotely close to the modding community that osu has let alone some sort of actual ruleset, and yet there are a ton of very good maps/charts out there for those games. Everyone in those communities is completely free to use or abuse features in any way they feel like and yet if you look at what the good players play, the maps are generally all very well done. All we really need is a set of guidelines at best.
A good example of someone from the stepmania community who was famous for their charts was NVLM_ZK, a japanese stepcharter who regularly created charts that broke many of the general guidelines people followed. Yet his maps were still fun for a lot of people (even if they barely made sense most of the time).
Jackhammers and other patterns seen to be "abusive":
Jackhammers have always been controversial. Many players hate them, because they are very difficult, yet they are often used. Despite being difficult, there are times when jackhamers are appropriate, and should be allowed, even if they are to the point of being ridiculous. If a map "abuses" jackhammers, maybe it should be accepted, rather than ranked (though frankly I think the distinction is pointless, other than to maybe serve as a warning of "hey, this map is actually hard, or does something that might piss you off"), as long as the timing is correct and there aren't any glaring other problems.
I see the number of keys as a sort of "sub-gametype". Each key number presents different mapping patterns, and subsequently forces you to think slightly differently when mapping for the number of keys (5 and 7 have a middle key, 4, 6, and 8 don't, etc.). If you're going to map for 7k, you should at least include 2 difficulties for 7k.
As far as holds spanning BPM changes, I think it's a terrible idea to make something unrankable due to limitations in the software that should eventually be fixed.
