if you dont want to play it live have you considered the Line 6 guitar port? thats fully upgradeable via line6 website downloads, they are quite cheap too, $80, if you subscribe to their website for a small monthly fee, you can download lessons, most of the line6 equipment is upgradeable, and you know they will still be around in 5 years time. They do have some technical backup issues, namely they never answer your e-mails but if you can read an instruction manual then there wont be any need to contact them.
If you want to play it live and you are fussy about your valve amp tone then i would’nt recomend a multifx unit, go for quality individual pedals, if anyone tells you a Boss GT6 Multifx chorus effect is as good as a Boss CE-5 pedal, then they need their ears testing, and the differences are more noticable at volume, the MultiFX gives an overall impression of the sounds featured, they can not match the quality of individual pedals, ive got an ME-50 and the effects are good, but they dont sound exactly like the the pedals featured, there is a rat turbo setting, and it sounds nothing like the turbo rat, and it goes for all the other multifx units ive tried, they are ok for the money, but i dont like playing them live, at low volumes or maybe through a PA they sound good.

We have been having a discussion about these multifx, ive not seen the Mode soundworks before, might be a US only launched product, it looks ok from the description, by why would you want it upgradeable? why not just go for mid priced Boss Multifx unit? or a line 6?? tell us specificly what you want to use this for? and i would hold back on the GNX4 im sure there is a new model on the way, i read an article in my magazine this month.
Anyway what is it for and what is your budget? what gear do you use too?
Lee