In terms of fairness and providing more fun for all type of players, I think it is a great idea. Now, realistically speaking, I am not really into taiko mode, but I could give a few suggestions.
Now lets see.... osu! standard has the most achievements because it's "main" mode. Catch the Beat and Taiko are special modes, so they should have some kind of special achievements, so to speak. Former already has "collect x number of fruits" achievements, so Taiko should have something similar, as in, related to the mode itself in some way.
Here are some things that comes to mind(not necessarily implying that all of them should be implemented):
- 1,000 combo
- 3,000 plays
- 10,000 plays
- 25,000 plays
- 50,000 plays
- 1,000,000 large red note hits
- 5,000,000 blue note hits
- 10,000,000 red note hits
I certainly don't have a clue about how achievements are made, but if there is someone willing to make them, sure why not.