I can think of just a few reasons for this interesting design, although all of them are rather niche/low-uptake-rate reasons:
1) People such as I who want to be able to listen to DSD with a bitperfect signal path, if this new amp's integrated DAC can accept bitperfect DSD and convert it to analog before the integrated volume control (which must be analog) that sits before the amplification stage. This provides a niche benefit for people who otherwise cannot listen to bitperfect DSD with any of the, "perfect companion streamers," as stated by WiiM marketing.
2) People who use external, digital room correction modules like MiniDSP Flex with digitals inputs/outputs or (like me) DSPeaker Anti-Mode X2D, which also has digital outputs only, so people like us need a separate DAC anyway from the streamer's, and an amp with integrated DAC would reduce clutter.
3) People who want more analog inputs than are included in the regular WiiM streamers.
4) People who use an external DAC or room correction module with balanced outputs (assuming this amp has balanced, analog inputs, that feed straight to the amp, or the volume attenuator if it is analog).
In other words, my interest is heavily piqued, but I suppose I'm weird, and that's okay by me.
May also be a nice option for owners of pure streamers from competing manufacturers. Imaging the conquest play where someone who owns a Bluesound, Eversolo, etc. buys one of these amps to go with their streamer, and then over time, decide to replace their current streamer with a WiiM Ultra, or its follow-up that still has the same form factor.
-Ed