I was thinking of making TL4 stuff a bit of a rarity in my setting - not hard to get, but expensive. I was thinking making TL4 worlds offer TL4 stuff at twice the price, but normal price on TL5 worlds. Seems like it'd work?
It won't break anything, no, though you may want to be a bit careful if the group doesn't have a Biopsionic and is reliant on pharmaceuticals for their healing.
+Kevin Crawford Any suggestions on making TL4 stuff hard to come by without running into that healing problem?
Just leave pharmaceuticals book-price and you should be fine. Warriors work perfectly well with cheap slugthrowers, and Experts won't be too stressed to afford most tools.