Disagree with OP points:
1. Software compatibility is not issue, last few Nintendo handhelds revisions didnt had 100% software compatibility, so point that you cant play few games while you can still play 99% of games is not deal breaker and never was for Nintendo.
2. This is similar point like software compatibility, 99% of game has/will have classic support controls, not isues in any case.
3. This wouldnt be any problem, this would be just one low price point revision and one offer of "Switch family" for people who want cheap device that they would play only in handheld mode. You want TV Mode, multiplayer, Labo, 1,2 Switch..no problem, you can easily chouse more expansive Switch revision that will offer all that.
Some people look at "Switch" only like one device with hybrid concept, "Switch" represents concept but at end its just a name, I am pretty sure that Nintendo at "Switch" looks like hole platform that will have multiply different kind of revisions instead of just single device. Namings like Switch Mini/Pocket/Go/Lite/TV...despite point some of those revisions will not have full hybrid concept will not stop Nintendo from releasing that kind of revisions, for them is far more important to expand apealing and price points of "Switch family" than stick just to one naming and concept, at end most important is that all those revisions could play Switch games (at around 99% of them).
People need to realise that Switch is only platform for Nintendo going forward now when 3DS dies, and Nintendo would definitely want to expand Switch appealing on market in any case and that includes different type revisions and price point on market, for comparision Switch currently has only one version that costs $300 while 3DS covers price point from $80 to $200 with different type of revisions, Nintendo will want to do something similar with Switch especially when 3DS is next year and they will not have low price point offer on market any more, and low price point Switch Mini/Pocket would perfectly fit.
But why Joy-Con less? Simple, built in controls instead of detachable Joy Cons (of course that wouldn't be only cost save) would gave biggest cost save for Nintendo and that would automatically means much lower price point compared to current version. Such a device would be aimed to be personally device, in other words device per person instead of device per house, so cheap Switch version for people that want only handheld play or for parents that would buy device per each of their kids. This would not be issue in any case simple because you would still have regular Switch if you want full Switch experience but for more money offcourse.
Also its not only point about low price point Switch Mini/Pocket, but Switch TV is also possible, it would basically be something similar like Vita TV for people that wants only home console play.
