My answer is very specific to my situation:
Never, and here's why. In January '08 I suffered a traumatic brain injury. Though my recovery has been, in other people's words, 'miraculous' I still notice some changes. I have trouble with my short term memory.
What this means is that I have trouble with new electronic/mechanical things, like the new cable tv setup we got, and driving my husband's new truck. (I remember all the driving rules, so I do remember how to drive, but I don't drive without him next to me. In fact, when he's driving I still have to ask him the proper procedure for adjusting the heat, ac, radio. The brake, accelerator, turn signals are in the usual expected places, so I've got that)
So, I can only assume if I got a new sewing machine of any kind, I would have trouble. I'm very fortunate, all the sewing knowledge I had stuck (it's been up there 40 years or so), and I have a very reliable Viking 630. Learning FMQ is still a challenge, but I'm dealing with a machine I've had from the 80's, so that's one thing I don't have to learn.
In fact, I have 6-7 630's I've bought over the last few years, can you tell I don't want t be without my machine?
Mt husband has rigged up my sewing room, and table, so that FMQ is as easy as it can be, and I don't feel the need to justify a longarm, so there ill not be a longarm added to the mix