swappable cpu, 25mhz? with 040? 183mhz ppc? sure go for it, pull them in from other models. RAM? 36MB ain't a bad limit.
Amazing to think it was only four years later it was truly bested by another incredible series of PowerBooks, the Wallstreets - a refinement of exactly the same idea.
The 540c was damned near 1992's Quadra 950 flagship tower, but portable, just 2 years after it.
And given everything was heading portable, and is now, that's why it's my pick.