Well the Malcador does require that your Marines be in 30K
By the letter of the rules, Escalation only covers the units included in it, but I can't see that holding up for long. There are a host of other lower powered super heavies that would work much better with 40K than the ones in the book.
I'm sure either players, or GW will be happy to sell you another hardcover with them. Off the top of my head:
Maldador
Macharius
Heirodule
Scorpion
Cobra
Battle Fortress
Gargantuan Squiggoth
Brass Scorpion
Tigershark AX-1-0
These are all lower in power than some of the models from Escalation.