Shimano Nexus 3 upgrade? Nexus 8 or Alfine?

[E24man]

Any Shimano gear hub geeks out there please?

I'm considering a new bike that has a Shimano Nexus 3 fitted and wondered how easy/hard/impossible it is to upgrade it to a Nexus 8, Alfine 11, or any of the other Shimano multi-gear hubs with more than 3 gears?

Any advice gratefully received.

Edited by E24man on Thursday 1st October 08:31

[E24man]

I had read about the Alfine maintenance; is the 8 speed Nexus easier to live with?