I have somewhat of a sweet spot for AT boards despite the obvious disadvantages, it reminds me of my first PC. But yeah, I too would be a little disinterested in 440EX and 440LX chipsets because they can't do more than 66MHz FSB. I wonder if you could use any of the later Mendocino or even early Coppermine Celerons with slotket adaptors on these, could be interesting.
AT Slot 1 and Socket 370 boards were not really a thing in my country and to be honest I don't see them pop up in discussions a lot in most European sites or auctions, so perhaps it was more of a US thing?
The only slot-1 Baby-AT I've acquired in person is a Micronics Twister 440LX. It has AT+ATX power inputs and the older DIN keyboard port like super 7 boards typically had.
I've tried it with Mendocinos but it didn't work - it freezes during POST at the part where it's trying to tell you the name of the CPU. It displays no name, just "-98MHz" and freezes.
I wasn't able to find any BIOS update online. It doesn't help that the manufacturer went out of business forever ago, and it's not from a well known enthusiast brand so there's very little info or support for it on the internet.
Back in those days, I remember seeing a few Slot-1 Baby-AT boards listed for sale here in US. One I remember looking at closely was an AT version of the Asus P2B.
The reason I wanted Baby-AT was to minimize the upgrade cost. The Slot-1 platform was so expensive that it defeated the purpose. Super 7 made more sense for someone trying to save money, and I guess other people felt the same way given the rarity of slot-1 AT boards. Super 7 AT boards are a lot more common.
The cost sensitivity of late Baby-AT builds may have made this a good niche for 3rd party chipsets like the board that the OP posted. But the cost of the Intel CPU remains, so it was still more expensive than building a super 7 machine.