Honestly, what's the point? As far as I know, warpgates are superior in every situtation. So why even make it possible to do something that is a complete waste of time?
IMO after warpgate research, gateways should build units faster than warpgates, maybe even at a reduced price, while warpgates - the opposite. That way if you want to warp in 20 adepts in someone else's base for an allin, it takes longer to cooldown and more money, but if you want to make units to defend at home they are cheaper and easier to build.
Less allin play, better core army availability. This obviously would have to be balanced as being able to get like 50 adepts really early would still be a guaranteed a click win across the map, especially on small maps, but surely it's an idea worth considering?
With this kind of rework you could probably fit in some gateway unit buffs where needed to make protoss able to have gateway core armies.