Except you use a blower style GPU it makes sense to put the I/O at the bottom so you won't have anything interfering with the exhaust of hot air at the top. I like the DLH21 design but if they would have flipped the I/O to the bottom they could have used a larger exhaust fan on top which I guess would have been overall better thermal-wise (IMHO).
Concerning accessibility I agree the top I/O is more convenient but there are also workarounds for bottom facing I/Os.
Depends on personal priorities I guess.
Ah, good point on the type of GPUs(I just googled it up haha!). I'm still getting myself familiar with the latest GPU tech(will be using my good ol 970gtx until the current 30x0 are more easily available). In fact, I kinda bought this case on a whim as my current mobo suddenly died last week. Since I was planning to replace with an ITX mobo really soon, and chanced upon a local seller who had stock of the DLH21(it was considerably cheaper than getting any of the other taobao cases that I have been eyeing for a while), but I thought I will use this as practice for my first SFF build until something smaller/better comes along.
For now, this case ticked all the right boxes for me, ie. smaller footprint, top/front I/O, dust filters, no need for any fancy risers, space for AIO(I'm gona try to see if my current 280mm can fit in it!).
I seem to remember seeing a review where they fitted a larger fan above the I/O compartment at the top, can't seem to find it now but I should be getting the actual case in a couple of days to see for myself.