You can remove SVs by changing all green timing points to x1.0, and changing all BPMs in red timing points to the same value (without doing note re-snapping); the only problem is the bar line if you are using it in your skin.
If you don't care about hitsounds/keysounds, you can also just remove all timing points except the first red one to do it faster.
Implementing constant scroll speed as a mod is not hard, just make the client ignore both BPM changes and SV changes in the beatmap. If the player is using BPM scale, use the most common BPM in the map as the base speed.
That mod shouldn't be unranked, instead, when looking at leaderboards, there should be an option to easily filter mods out (already possible if you use a script for seeing the site, though a considerable amount of players don't have those scripts installed). Also, it shouldn't give a pp penalty, since the star rating system doesn't account for SV changes; instead, either the difficulty system gives a bonus to star rating when maps have difficult-to-read SV changes, or make a ranking system where the players are ranked in more than 1 dimension, including SV-reading (like osu!stats or pp+ in osu!standard).
If you don't care about hitsounds/keysounds, you can also just remove all timing points except the first red one to do it faster.
Implementing constant scroll speed as a mod is not hard, just make the client ignore both BPM changes and SV changes in the beatmap. If the player is using BPM scale, use the most common BPM in the map as the base speed.
That mod shouldn't be unranked, instead, when looking at leaderboards, there should be an option to easily filter mods out (already possible if you use a script for seeing the site, though a considerable amount of players don't have those scripts installed). Also, it shouldn't give a pp penalty, since the star rating system doesn't account for SV changes; instead, either the difficulty system gives a bonus to star rating when maps have difficult-to-read SV changes, or make a ranking system where the players are ranked in more than 1 dimension, including SV-reading (like osu!stats or pp+ in osu!standard).