I don't actually care for tech spread/sharing/trading being an important mechanism. I prefer the Paradox standard, where one faction may be very, very far behind the current tech leader and tech spread is passive process with limited benefits except in the most extreme uses (conquer Constantinople in CK2, hoard MPs and westernize early in EUIV, inventions in V2).
When tech trading and sharing is an important and active process, invariably I see a tech leader emerge, then their friends become tech leaders/equals, then everyone else gets stomped or gets assimilated into the tech hoarding power block. It's, frankly, stressful rather than fun, because you have to find ways to buy tech or have it shared with you or you risk annihilation down the road because you didn't get into the Western club or it feels like an impending doom if you start too far away to jump on the tech bandwagon. Sometimes games implement these mechanics in such a way that you can eventually recover through aggressive trading, or more often through some kind of seize tech during conquest mechanic. I don't think I've seen a game that made tech trading/sharing actually reduce tech disparity overall, though they do tend to benefit human players who can plan around it more than AIs that didn't start in advantageous positions. These games often have a synthetic feel to technology, too, where everyone ends up using the same techs at the same time or close equivalents.
From a realism standpoint, tech trading doesn't make much sense. You can gift computers to China, but you can't make them upgrade from Windows 98 to Windows 10. Technological development is as much about implementation as it is simply inventing a tool that is economically viable. I hope Stellaris will keep things indirect and have an effective research rate that keeps the starting factions relatively on par with each other naturally in terms of total techs, though not the specific techs they have at any given point. I like the idea of tech spread through sending scientists to study wreckage and debris.