Just pulled down the latest Communitas 3.17 version for Civ 5 BNW and Played the French. On version 3.16 once I researched the Gatling guns I could upgrade Musketeers & Arquebusiers to Gatling guns since they are classified as Archery units.
In CEG version 3.17 Musketeers & Arquebusiers are no longer up-gradable, but Crossbowman are upgrade-able to Gatling guns. So this looks like a feature regression. And by not upgrade-able I mean they will not upgrade to musket-man or Gatling guns. They won't upgrade to anything in the Industrial Era.
Repro Steps:
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1.) Install Communitas 3.17 into the Civ 5 mods folder.
2.) Install IGE latest version into the Civ 5 mods folder.
3.) Start a Mod game in the Industrial Era as the French.
4.) Use IGE to give yourself the tech updates necessary for Gatling Gun (Steampower), and 2000 gold to purchase unit upgrades.
5.) Use IGE to give yourself a Crossbowman, a Musketeer, and an Arqebusier.
6.) Attempt to upgrade the Crossbowman, and notice that it will upgrade to a Gatling gun.
7.) Attempt to upgrade the Musketeer, and notice that it will not upgrade to anything (no upgrade button).
8.) Attempt to upgrade the Arqubusier, and notice that it will not upgrade to anything (no upgrade button).