Chug and Phanteks both indicated April, frustrating wait but think worth it...
I've still not got them on order unfortunately so might be more like end of April/May. Not for a lack of trying I promise!
...are there any other good mATX cases with glass side panels about?
In terms of cases that are glass and ONLY take M-ATX, there aren't many at all. There is the Lian-Li PC-O6SX which is a crazy price and an awkward size. I highly doubt you'd want something this expensive with your 1-year old's proclivity for PC toppling haha!
There's also the Cooltek VR2, RM3, and you could also check out the W2, which is actually ATX but is still very compact. An M-ATX board wouldn't look swamped in there at all, plus it gives you options in the future if you did scale up.