It makes sense to me that Ruger would design a gun that may be upgradeable to test the market with a single caliber offering that they could add to later. This will allow them to put out the numbers on the current offering while planning for the future on others. If both 45 ACP and 9mm were out today, I'd need to choose which to buy first. It seems a given that sooner or later I would have both. Contrary to what most would want, I would also love to have one in 380ACP.
Why 380? Because I have had my 21 year old daughter hooked on Browning guns since I bought her a BLR 22 when she was around 10. I wanted her first gun to be special and it was something I always wanted for myself but could never justify spending that much money on for myself. Her Browning collection grew and eventually added a 1911-380, which is the perfect size for her small hands. The 380 is an economical round to shoot IF one reloads. I am fortunate enough to have a Dillon 550B, so it reloading not a problem. I just need to be sure to avoid losing my brass. Her first background check was made to purchase a HiPoint 380 carbine. While lots of noses are going high in air while thinking first gun purchase and hi point, I am not a gun snob and give credit where it is due. It is a great carbine and since no other 380 available that I know of, Kudos to hi point. Having said that, I would definitely buy a Ruger if available, but do not foresee that happening.
To each their own, but I have no interest in 40 or 10mm, largely in part because I am not set up for reloading them and the bullets would cost as much as the 45 caliber, which are double the weight and cost of 380 and 9mm. I also already have a few 45ACP guns in the safe. A 45 version with magwell adapter for 1911 and magwell adapter for a larger capacity double stack would be sweet. I am content with using 7 round 1911 mags, but am sure the masses would love volume.