there may be no business excuse in your mind, but as a long time wanter of a product like you are describing it is merely a pipe dream. If not mental or just a lot of teasing of ones self it just is not going to happen.
I believe Jobs and Gates decided to leave certain areas alone. Ie Apple does not sell graphics and games. windows does not push for t-bolt or firewire.
Since it has worked why mess with success. you won't see windows pcs with inaccessible ram and hdds as the norm . Windows allowing an external drive boot with ease not that common. Doing this forces many people to have 2 computers for work.
I agree, though I see where the OP's coming from. However, IMO, if such a Mac was going to be available, Apple would have surely offered it before laptop sales overtook desktop, ie. well over 5 years ago.
To the OP: yes, Apple could still offer such a Mini Pro. Most probably it'd sell well. But look at their activity in recent years: Macs that continue getting thinner, smaller. Increasing focus on mobile devices. Neglect of their Mac Pro range, et al.
There's nothing to indicate that they'd place a new desktop Mac in between their iMac & Mini lines at this stage. They'll also not want to risk cannibalizing iMac sales. Best bet is a smaller Mac Pro in the coming weeks, but I'd expect a starting price similar to now, about $2,500. Too much for my needs.