Mirrorless doesn't need to have the super short lens register they do.... It's all up to the designers. So, yes, in that respect, mirrorless and DSLR can be the same.

In fact, there's talk of Canon and Nikon "full frame mirrorless" and it's something I think they should very seriously consider: Canon should use the same EF mount and 44mm lens register that they do with their DSLRs and film SLRs.... And Nikon should use the same F-mount bayonet and 46.5mm lens register that they do for their FF DSLRs and film SLRs.

There is no reason to use a super short lens register on full frame cameras (18mm is common on APS-C), because....

1. With full frame, in particular, it does little to reduce the size of the lenses and camera . Look at the full frame Sony MILC and the lenses used on them. Not much to be gained, so why do it? (OTOH, it DOES allow APS-C and micro 4/3 MILC to be significantly more compact)

2. Another motivation they might want to consider... rather than create yet another series of lenses, use the ones you've already got without need for any adapters (which further increase lens size). As it is now, Canon's got EF lenses, and EF-S lenses... and a few EF-M lenses. What we REALLY don't need is EF-M-FF lenses too! They are struggling enough to just building the EF-M series (five + years in development and still only 8 or 9 EF-M lenses? most of which are "kit" quality zooms?), without having to start putting together yet another series of lenses! it's a little different, but Nikon has FX lenses, DX lenses, though they apparently hve given up on their Nikon 1 lenses. So if they insisted on creating another series just for their FF MILC camera, they'd only have three lens series (compared to Canon having four). Besides the confusion that it would create (isn't there enuf of that already, needing Nikon/Nikkor compatibility charts?), they'd also be undermining sales of the two most successful and comprehensive lines of lenses made by any modern manufacturer. No need to shoot themselves in the foot!

3. There also are some optical challenges to making ultra wide lenses work on a very short register camera.... which could easily be avoided by simply sticking with what already works.

A MILC that uses their existing lens register... that can use all existing 60 or so FF capable lenses Nikon and Canon each offer... could have all the other features of a MILC: EVF, high frame rate, silent shooting, yada, yada.

In fact, it makes A TON OF SENSE... so they probably won't do it