This past spring I looked into/at the S-919 (already mentioned, and surprised to see that because) last I checked, they were more of a proof of concept/sample/for rebranding/integration and so a direct order piece from iStarUSA. I did send an email, and they may have even replied, but I never followed up.
I also asked iStarUSA about their S-919 case and the guy responded to me saying that they do not have any in stock, but can make more with a minimum quantity order of 25. He didn't tell me the price unfortunately :'(
In my extensive search, everything with hot swap bays is either a full tower case or a mini itx case. For whatever reason it is very difficult to find a Micro-ATX case with hot swap in the US.
--Micro-ATX Cases:
But for what it's worth, this is what I've found (though buying them is difficult in most cases):
-Chyangfun CFI CH-C4000N
-ChyangFun CFI-A5000 or JMAX JX-FM500B (
CFI-A5000 - Chyangfun Industry Company) or (
JMAX JX-FM500B|PCパーツ・周辺機器の総合代理店 マスタードシード株式会社)
-CD LOG A500NCB Micro-ATX case
-iStarUSA S-919 (has 9 hot swap bays to add your own hot swap enclosures...requires bulk order)
-Lian Li PC-A04 (might be able to add Lian Li BP1Sata hot swap to the back of the internal 3.5 bays but not sure)
-Lian Li V354 (same as the Lian Li PC-A04)
-Lian Li PC-V600FB (can add more Lian Li BPSata backplanes)
-Lian Li PC-V650B (same as Lian Li PC-V600FB pretty much)
-Lian Li PC-M25 (says it fits both mini-itx and micro-atx)
-iXSystems FreeNas Mini XL Chassis (if you can find just the chassis)
-U-NAS NSC-810A (micro ATX version of NSC-800/810)
-Silverstone CS380 (micro ATX mid tower of DS380)
--Mini ITX cases:
-iStarUSA S-915 and S-917 (S-917 will probably fit a micro-atx with some modding)
-iStarUSA S-35 or S-46
-Lian Li PC-Q26 and Q25
-Lian Li PC-Q35
-Lian Li PC-M25
-Lian Li PC-TU200
-Silverstone DS380 (obviously)
-Silverstone CS280
-Silverstone CS01-HS
-Silverstone Rackmount RM208-Mini (CS-RM208-Mini)
-Norco ITX-S8
-U-NAS NSC-800 / NSC-810
--Mid Tower Cases (these are the smallest ones I could find that also had the most 5.25 slots to add hot swap bays into them):
-Sharkoon REX8 Value (small mid tower with 8 external 5.25 bays)...can be found on amazon.co.uk or amazon.de
-Sharkoon T9 Value (small mid tower with 9 external 5.25 bays)...can be found on amazon.co.uk or amazon.de
-Silverstone CS380
-Travla T2280
-iStarUSA D-3100HB, D-380, E3M8, or D-A380
-iStarUSA D-260HB, D-250, or D-265
-XCase EasyStore S16REH, X339F, or X348
-Logic Case SC-43400-8HS or SC-43480B
-Cooler Master Centurion RC-590
-Azza Helios 910
-Aerocool XPredator X1 (with some modding)
-Aerocool Strike-X Advance
The iStarUSA S-919 seems like the perfect fit for micro-ATX cases but when I inquired to iStarUSA Customer Service. They only were doing bulk orders of 25 units. This was back in 2015 though so it might have changed now.
I hope that helps anybody who is looking for something bigger than a mini-itx case, but smaller than a full tower, and that can offer hot swap bays.
UPDATE:
-U-Nas has created an update to their popular NSC-800/810 chassis. They now make a NCS-810A chassis that fits micro-ATX motherboards and retails for $219.99.
U-NAS NSC-810A Server Chassis (Power Supply Not Included)
-Silverstone has also released their Silverstone CS380 that can fit micro-atx boards and is a larger mid-tower version of their DS380.