I'd certainly like to see ones that are minimal cost trialled on the PTE or on a Firestorm world. The PTE is good for finding bugs (although not all are discovered quickly - for example one found today) but not so good for PvP changes as there is minimal competition and PvP. Certainly new POI's or changes to how they work could be trialled.
I'm fairly sure from the discussions I've had that there is an internal list of suggested changes. I'd expect a rough costing in terms of hours for each change to be on this list. Obviously they're not going to share the costings but as you suggest, some indication of it being too costly or not technically feasible would be good.
But this is nothing new! It's been said many times.