My idea is to, after the 1240 gunpowder event, make a lab similar to the alchemist's guild or university available to construct in large cities that takes 10+ years to build and has a high construction cost. This building would open up the building of a basic gunsmith in that city, with a TLR normal buildtime/cost. After this building is completed, another smith could be made that opens up grand bombards. At that point, another, much more costly and long-constructing "lab" would be available to construct that, once made, opens up construction of basic cannons. The gunsmith that builds cannons would unlock another lab, closer to construction time of the original lab but still as costly as the last lab built which would allow military barracks to be built that produce the handcannoneers. The last 2 labs, which unlock the barracks that produce arquebusiers and matchlock-level guns respectively, would be more costly and longer building than any of the earlier ones and require a royal arsenal to be made that itself requires a lab to be made.

All the base gunpowder tech labs for the advanced gunpowder would be available to make directly after 1240. However, at dates such as 1410 for those players/computers who don't want funds and time tied up in expensive labs (which really represent research) the higher techs' prerequesite productiuon structures, weather it's handcannons, bombards, matchlocks or Basilisks, would become available for construct, still in the "vanilla" TLR build order.

All this would allow players who want a major technological edge to focus on gunpowder research earlier than historically ocurred, but at the same time keep people from getting matchlocks by 1300 ala vanilla MII:TW due to long-constructing and costly labs. Not only would these labs make your large city ques unable to construct anything else during that times, a significant portion of your coffers would be tied up in the lab's construction, putting a dent in any current war efforts and possibly letting you get overrun. Factions who wait for events to trigger lab-free gunpowder might get it slower, but wouldn't have to worry about high-cost labs.