Call me a cynic but I doubt running Alliance Raids in an undersized party is going to be added to the game anytime soon, since many encounters across all ARs are designed for 3 teams in seperated spaces. For example the triple-catwalk fight in Labyrinth of the Ancients which requires at least 5 players on all three platforms. This Raid would be impossible to finish alone and changing it to be would require significant restructuring efforts. However, the ability to purchase items with coins would at least fix, or circumvent, your primary issue; bad luck making it so that the items you want or need simply do not appear, by allowing you to eventually get what you want by just clearing the content enough times. And it would be less effort to implement, or at least I assume so, since I cannot, and don't want to, imagine that placing a merchant somewhere in the world that sells these things would be significantly more demanding than compiling a few .xml-tables.
I have grinded The Tower at Paradigm's Breach to exhaustion because many costume pieces just would and would not drop, and frankly I believe I wouldn't have bothered if I had anything else to take care of in that time period, and if I wasn't aware that these raids' populations will likely plummet upon the release of Endwalker and the Lv.90 ARs, effectively making those equipment pieces impossible to obtain in an appropriate amount of time in only a few weeks from now.