So by 'size' of the expansion, are we talking about the size of the 'source' contents folder you point the expansion builder to, or to the size of the resulting XPN file (XPN files are effectively compressed zip archives, so will be anything from 25-40% smaller than the source folder).
If there is a 2GB limit, then it definitely does not apply to the content folder size, as I sell several expansions that exceed this (2.4GB being the largest). But all my XPN files are smaller than 2GB (largest is 1.75GB).
The Akai 'Vault' expansion is around 6GB, so there's clearly no limit to the size of the expansion once it is installed, as it's just a folder of WAVs and XPM files. I assume any file limits are imposed during the installation process, where the MPC Software has to extract the contents of the XPN file.
Either way, if it's just for your own use you can 'manually' install a huge expansion into the MPC Software, i.e. just copy the standalone expansion folder to the relevant place on your disk. On a Mac user expansions can be installed here:
/Users/andy/Library/Application Support/Akai/MPC/Expansions
On a PC:
C:\ProgramData\Akai\MPC\Expansions
As long as your Expansion.xml file is configured correctly (the 'identifier' should definitely match the folder name, image file correctly entered etc), then the MPC Software will pick it up the next time you launch it. If you have expansions already installed there, take a peak at how they are configured.
My article about
creating force expansions explains the set up of the XML file. I'd probably stick with using the 'reverse dns' style folder names, i.e.
com.whatever.yourexpansion
and have the identifier tag in the XML file match this.
If I get time I'll investigate this to see if I can find the actual XPN file limit, and will update my
MPC Expansion Guide accordingly.
2GB the limit of 32 bit systems, perhaps this is related:
https://en.wikipedia.org/wiki/2_GB_limit