Wow! I had no idea the 8087 was such a complex beast.
My exposure to microcode was with the old Gould SEL 32-bit mini-computers I worked with in 1980. They had an add-on 'floating point array processor' from Floating Point Systems (aka a 'vector processor'), which one programmed using pipelined microcode. You loaded one vector (array of samples) as first input, then another one (same) as second input.
You could do an add, a multiply, a load, and a store in one clock (IIRC), so you had to 'prime the pipe (the instruction pipeline) then run the loop, then 'empty the pipe' to pop the last results out.
Immense fun for this bright young novice programmer (21yr old-ish), who had been dropped in the deep end with FORTRAN, assembler, and this microcode, and not much more support than a (very good) set of manuals!