Add "Equipable" box to Trading Post Filters
That would be something better than we have, but I still prefer the oft-suggested idea of having an armor weight filter. Your way would mean the Mesmer would have to slog through it all for the Guardian, instead of just saying “show me the Heavy!”
I’d love to have an equipable weapon filter, though, as you point out. I haven’t seen that suggested before. So long as one can still freely select any level, that part’s golden.