Removing a score multiplier from a mod? That's absurd;
http://osu.ppy.sh/p/beatmap?b=39076&m=1 -- I have honestly memorized the chart of Saitama for god knows how long.
In truth, there is no way to completely block out all loopholes for exploiting some of the mods, we can only lessen them.
We never know that some of these haxed replays may have been a result of actual memorization and was played fairly. Then again it is almost impossible to find the difference between a replay that was played with memorization and a replay that was played with an external visual gadget.
BUT, we can, however, detect those that are using 3rd-party programs to 'aid' them in these scores. Since this is actually a possible detection, it's feasible to purge those.
The mods were created to make things hard, and a score multiplier is a worthy reward for using such.
The fact that one has to still resort to either memorization or an external visual device actually increases that difficulty already. It's a different case for third-party programs though, as basically you don't have to spend anything monetary and require less time to be able to achieve scores like that. In the case of having an external visual device, it's no different than the logic of one person having multiple Pokémon games of different versions having an advantage against those that only have 1 version.
I know many that have external visual devices, but I don't ditch them for that. Well, yeah maybe I get a bit mad, but not to the point that I find it eligible for reporting.
To be honest I have actually done this once: http://osu.ppy.sh/p/beatmap?b=42796&m=1 . I got this score by simply looking at my DS Autoplay this song while I'm hitting the keyboard. But did you actually know until I told you this? It's basically almost impossible to tell, what can you do about it. Would you then conclude that I also look at another screen while playing Haya Saitama2000 and accuse me wrongly?
Point being: unless you can suggest some real way that we can differentiate players that memorized and players that are using external devices, I don't think it's feasible to do anything about it at the moment.