.... The cross-over point in price vs capacity for SSD isn't here yet, but shouldn't be that far off into the near future. ....
I used to marvel at how small 2.5" drives were, and could still hold 1Tb, then 1.8" drives came along.
My recent PC build I used a M.2 Samsung SSD only because it was the same price as any other 256G SSD, and it's speed was 3x faster .. so why not.
You could probably shoehorn 8 or 10 of those sticks of gum M.2 drives into a 2.5" form factor.
What would be nice to see in the immediate future is a 2.5" form factor using a M.2 SSD, the resultant space saving in the 2.5" case could house a large battery that could power the device for days(not hours or minutes), easily house GbE, and AC Wifi connectors too.
As long as the price of those M.2's drops as quickly as is happening for conventional SSD form factors, the future may come even sooner than the quoted "not far off"