Andrew, as usual that is first class work!
I have maintained that a significant part of my shopbots quality is the 1/2" aluminum bed for the table. You will find the same thing, a reliable, consistent bed you can attach a spoilboard to, or vacuum table, or dedicated hold fixtures, or... in your case who knows what all you will come up with?
The ALS "Aluminum slab" makes a lot of setup better/easier than the bots I use that dont have it.
Now the bad news, beginners will gouge the table if the spoilboard is not thick enough. I have never dug into the ALS, but I have ruined my share of spoilboards when Z "went south" or the bit slipped in the collet. An exposed aluminum bed asks for a gouge when X and Y are in the wrong place when Z wants to go south. Spoil boards are easier to replace and cheaper than aluminum. I suggest you might want a "sacrificial" board on top of all that shiny new metal
Just my musing- but for the folks looking at putting in an aluminum table, its a big improvement. You can buy them already made- they are called "optical breadboards". Look em up. They are flat too and pre-drilled with 1/4x20 holes on a 1" grid. There are metric equivalents for the metric users.
Andrew, thanks for the beautiful and inspiring work-
D