Heya guys, while it won't be enabled anytime soon on PBE, we'll probably be adding the Showdown mode permanently to Custom games at some point. I wanted to quickly give some context on why specifically the Showdown mode, and to set expectations of any other modes coming to customs.
Every year, events come around (EG: All-Stars, PAX) that either use or could benefit greatly from having the Showdown mode available. We want to help better support community events like these(or even just friendly trash talk between friends). Rather than having to run Howling Abyss customs with a "gentlemen's agreement", Showdown just makes it so much easier. The mode honestly wouldn't really hold up as a modern day RGM (it doesn't have the punch of a Dark Star or Star Guardian Invasion), but as an option available in the background for these kinds of events, we think it's worth. In which case, why not just extend it to all players as well.
This is possible because the Showdown mode has vastly lower tech barriers in the new client to making it available (it rests on the ARAM infrastructure). It's also effectively zero upkeep from patch to patch, unlike almost every other mode that requires non-trivial attention to keep up with LoL's changes. 1v1 Showdown doesn't really have any special/custom logic, it's a just a 1v1/2v2 that triggers for the victory conditions, so it's quite future-proof.
This obviously raises the question of, "Will any other modes be available in customs soon?" We don't intend to make any other modes permanently available in customs, so this will likely be a one-off. We do however still want to get Custom games working for each RGM while they're on during the weekend (they're not disabled by design, we do actually want them).
Showdown won't be available anytime soon™, but just wanted to give a heads up if files or strings start popping up on PBE.
insert obligatory "1v1 me bro"