Nasus and Veigar changes

Alright, I'm not sure if anyone has posted something similar in the past, so if I missed an article on this problem please let me know and shw me the link. In any case, here's the thing: I don't like the fact that Nasus and Veigar have the ability to stack damage on an ability/ability power indefinetely, for a few important reasons:

1. It can create a bad team experience for the team with the Nasus/Veigar if the said person just intends to farm and not help their team until they consider they farmed enough, but by then it might be too late if a lot of team fights took place and the enemies won a great lead because one player decided it's more important to farm in order to gain more power for himself, instead of helping his team when they need him.
2. In the event a team does well without the help of a Nasus/Veigar, and the said person manages to build A LOT of stacks (let's say a Nasus manages to build 900 stacks, I've seen it happen before), then the late game could become pretty hard for the other team to bear because they wouldn't be able to handle the Nasus/Veigar almost at all in the late game (unless maybe they picked a specific matchup that could work against a well-farmed Nasus/Veigar, with lots of CC and mobility for example), but even then, when teamfights break, a well-farmed Nasus for example can still pretty much instantly kill an enemy adc/mage, and it's even easier if they have Flash at their disposal.
3. It's not really too hard to farm with Nasus or Veigar. I haven't played Veigar myself, but I did play quite a few matches with Nasus, and I can tell that it's not really that hard to farm with him, unless the enemy team constantly ganks the lane with the Nasus in order to disrupt his farming, but even then the aly team can come aid Nasus in order to help him get his farm a bit more safely and then become a late game terror nevertheless. *) Also, I've once witnessed an enemy Nasus who was well farmed teleport into our base (it was late game), and killed both nexus turrets (when both were full health!), and the nexus in less than 20 seconds. By the time we recalled back to the base it was too late for my team to be able to stop him. And the worst part is that our team had the advantage in both objectives and kills. That was the game that made me realise that Nasus can make the enemy team's effort go to waste, and I don't mean this as in 'Nasus can give his team the potential for a comeback', this goes beyond that, as in 'Nasus can literally nullify the enemy team's efforts within less than 20 seconds'... that, I think, is something no one likes to see.

So, here's my proposed solution in order to solve at least these problems: Give a maximum capacity for stacking, that could be increased by champion kills (or even assists), and maybe even epic monster kills/assists. Like for example for Nasus: His q shouldn't allow him to stack more than 100 damage from farming at first, but if he succesfully manages to get a kill, then the cap should be increased to 200. Then after another kill, to 300, and so forth. This way we can ensure a Nasus won't have any reason to just keep farming all the time, and will feel inclined to help in teamfights more, and he will have to actually work for those stacks.

At least that's my opinion. I'll admit this might not be an objective opinion, but I'm fairly certain other people who have experienced matches with Nasus/Veigar on either teams will understand what I'm talking about.

Again, I'm not sure if this has been proposed already or not, but I think this will improve the way these champions are envisioned by the community, and make them feel a little less overpowered.

EDIT: Also, if this capacity increase were to work on assists, I believe the cap should increase less for assists than kills, since it might be a bit easier to obtain assists rather than kills. Like for example kills can increase the capacity by 100, and assists by 50, or 40. Also, some epic monsters like the elder dragon or baron are a lot harder to obtain than the rest (rift heralt, elemental dragons) and require more effort from the whole team, I think the maximum capacity increase should work the same way: for example, kills/assists on elemental dragons or rift herald will increase the capacity by 50, and kills/assists on baron/elder dragon will increase it by 100.

Also, the quantities don't have to be exactly the ones I've mentioned (I'm not a game-balance expert), it's just the idea that kills on champions value more than assists, and elder dragon and baron are more valuable and harder to obtain than elemental dragons/Rift Herald.