Now we should really get this discussion at the RPG-forum in the thread already there. As said, at the moment we discuss EXACTLY that point at the rpg.
We have to following proposal up:
1) only technology which is know by us or a knows civ is allowed
2) technology not know by us is punished with much less revenue when sold
(very rough, but the details seem to still be needing workout)
we wont delete the things we have now, but stall techs, like you proposed.
for example catalpults

presuming my proposal (to be defined more):
they could be build (i think our neighbors know mathematics?).
but the revenue will be VERY low (10%, instead of 80%). This way the prices will be higher. Also, as soon as we ourselves discover mathematics, the prices will be cut down to 10% of the previous sales-price.
now if catapults are sold now for 1000gold each, the seller woud get only 100gold each as profit. as soon as the fanatikans know mathematics, he has to drop the sales price to 100gold, and get 80gold revenue.
This way the seller is forced to use VERY high prices for imported goods.
Same would apply to resources we dont own.
The problem with that would be the tracking.
Now please(!) cary this discussion to the rpg forum, as many more people would participate in it then.
And we should have a discussion for each now rule-proposal. Not for all proposals in one thread (this is the stupid way we started it at the rpg-forum at the moment, and thats also propably the reason why discussion stalled

)