It's the same, you would have to set a time limit (generation) for "new tools" and people would just complain about doing it on that generation and not a previous one.
And even if you sort that out, there is still a possibility that you would still end up with a lot of complex bans and having a lot of pokemon in two different tiers with certain conditions. It would be a mess and make competitive battling very confusing and inaccessible, and to make things worse the list of complex bans would just pile up with each new generation.
It's just not worth it to get into this mess so that a couple of pokemon can be OU or whatever...
Under my rules, Blaziken would be the ONLY Pokemon this would even apply to, so why are you assuming this would get used so much? It would only come into play if they do something as stupid as giving Blaziken Speed Boost. Nothing else they changed is worth enacting what I described.
They've banned one Ability+weather and they'd only have one Pokemon in two tiers. Why is this so awful?
And the guy talking about Venusaur...what? Yeah, Venusaur didn't have Chlorophyll before but Chlorophyll Venusaur is OU, so there's nothing wrong with this situation. My rules would only come into play when they give a currently-released Pokemon something that turns it Uber overnight. They don't come into play just because they made Venusaur OU since that's a good thing if you ask me.
Yeah, you can't use Venusaur in a lower tier now but the point is you still can use him outside Uber, so that's fine. If you have a huge beef with a Pokemon you like getting better (but not OP) then...seriously, just get over it. Use a different Grass type in NU or whatever, or put Venusaur in your OU team.