Yes I would probably wait for MH3, but one thing I did to build up my Historic and Timeless collection was to buy packs from sets containing the lands that are staples in the formats. You could buy packs from KTK to have a higher chance at opening a fetchland for instance, which decreases the number of wildcards you would need.
The problem with buying packs from older sets is that they don't contribute towards the "gold pack". When you buy 10 packs from the latest standard, alchemy, or horizons/remastered release, you get a gold pack which is a pretty good value especially for building a timeless collection.
The cards will be a higher power level and more impactful, as they skip standard.
Plus if it's anything like MH2 it'll totally shake up the meta and change which decks are played, so also invalidating previous wildcard spends.
Unless you want to focus on Explorer, which won't be affected. In which case... Ravnica sets for a chance on a shock land and NEO for an above average pool of playable too (IMHO) would be decent choices.