I get that they wrote this “clarification” with regards to idiots who thought Street Peddler literally couldn’t do anything. But the effort to fix the issue is arguably dumber – and I can’t believe this is possible – than those idiots were in the first place.
Trashing a card as a cost for an effect can trigger all sorts of nonsense that can go on to trigger other kinds of nonsense before the effect has a chance to resolve. Trying to reference the game state at the time of trash (even the narrower case of “the game state as it pertains to that card”) is just a fundamentally bad idea.
E.g. Without even getting into fancy scenarios like SMC/Geist (and all the potential cascading triggers from there – Palana, Tech Trader, etc.), suppose I have a rezzed Test Ground (I know, lol) with one counter on it. I trash it to activate its effect. Can I now use that effect to “derez” the Test Ground that is already in the trash, because the game state at the moment it was trashed recognized it as an active, rezzed card?