The BTX form factor is taking a while to be adopted.  While not too many systems are being based on it, you can still find cases that meet the new specs, like the SilverStone TJ08, reviewed by TECHGAGE.
“SilverStone is back again with another great looking case, but this time it’s for you BTX users. The pure black case has a brushed aluminum surface, and is one of the classiest looking you can find on the market. Is the performance up to par with it’s looks?”

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