I believe the intent of this case is to be a sleek small form-factor NAS.
(a) It's not labeled as a NAS box -- although I'd agree that's all it's
well suited for; (b) many purchasers bought it for an HTPC and I mentioned the oddity of "excessive" drives bays versus missing options front-features as a consideration for non-NAS use.
As for motherboard ports, it's true that most top out at 4, but there are some which have six. More importantly, it's easy to add a PCI-E controller to have as many drives as will fit.
When I checked a few days ago, NE carried [i.e. indexed]
NO Intel mITX boards with more than
2 sATA-III ports, 1 AMD with 7 sATA-III and 2 AMD with 4. Let's not get into a II vs III discussion, but I only use III for non-ODD drives, which to me means there's only 1 m/b that merits this case's drive capacity on its own IMO.
PCI-e sATA controllers abound, a number supporting 4 III ports (or SAS) though many have limitations (particularly in the number of PCIe lanes supported [hence throughput]). With the single slot used up, gone are other options like LAN-teaming or working around m/b failures or limitations. The latter may not concern some folks, but I've had LAN-port and graphics failures on m/b's and always worked around them with spare slots.
(Mini-DTX theoretically offered 2 slots, but most boards either dedicated 1 or more to included features or dropped them. mDTX was also about an inch wider than required judging by ITX compactness.)
If you find such a board, be sure to let the rest of us know. I'm fairly certain you won't find a mini-ITX board with more than one slot.
I never mentioned mITX in that wish: mITX [obv.] only supports one slot, but I wish there were an prevalent standard supporting 2 slots in the general size/scale of mITX. Many mITX cases have a second rear opening for cable-attached hardware, so it wouldn't seem big leap to create some "maxi"[?]-ITX standard with the board extended for one more slot. But it doesn't exist, I'm not expecting it soon, and yet I'm not sold on mITX's single slot.
I suppose I'm left wondering what use case you are trying to fill here.
NAS, HTPC, light-weight computing -- anything that can be run on low heat loading hardware.