How much more space does an express card slot use up compared to a firewire port? It's an actual cavity in the body of the machine, not just an extra port... 🙄
Anyway, the last version of the 15" had expresscard, so it's quite clearly possibly. SD cards can be read by any number of different adapters - usb, firewire, or expresscard. Expresscard can't be replaced in this way.
Personally I wish they'd make a REAL Pro MacBook. Having just come from a Dell D830 with the following ports, I'm finding the MBP a bit lean:
PCMCIA Cardbus AND
Expresscard 54 (not just 34)
Firewire (albeit 4 pin)
3 x USB (and not spaced so tightly you can only use one)
Docking connector
Expansion bay allowing DVD drive, extra battery, or extra hard disk.
I want a MBP with Expresscard/54, FW800, eSATA (you can say whatever you like about FW800, I know it has some advantages but there is nothing to match eSATA for speed and there are LOADS of great, pro-level, eSATA devices out there).
Also please give me a Dell-style expansion bay to swap in an extra battery, hard drive, or DVD drive. Will the resulting machine be as slim as the current MBP? No it won't but I really don't care this is supposed to be a PRO machine.