One problem with a DAC-less Ultra streamer is that you lose the separate subwoofer output, which has been a valuable feature for many users.
And, as noted before, there is also the question of just how many streamer-only models would be sold. WiiM products, at their relatively low price points, depend on high volume production runs. WiiM is going to be ignored by many of the audiophile snobs looking for high end gear, so I question how many streamer-only units they'd sell.
But, those product decisions are made by WiiM management. It'll be interesting to see what shows up down the road. My guess is that their next product might be an Ultra combined with a power amp -- the modern equivalent of a receiver. I'd think a lot of people with passive speakers are looking for a one-box solution.