I would like to see all of the buses that don't have announcement systems to receive them, you could probably make exceptions, e.g. All buses Pre-2015 not to get them, which means that the following wouldn't receive them;
1-50, 171-190, 195-199, 201-215, 351-400, 401-425, 591-594, 841-850, 926-960, 1000-1050, 1141-1153. (Including buses in storage.)
Some of which have already had them in the past. Lets just hope the 15 plate Hybrids get them.
That's 259 buses, I don't think it would make sense to give these buses Next Stop Announcements given their ages, so I'd probably focus on the newest buses (That don't have them.)
I don't know what this gives to the table but I just wanted to point that out.