To use an analogy, I think that there are three different approaches to updating a house:
1. Rip out everything except the wall studs and roof, replace the plumbing and wiring, and rebuild back up from there with all new... everything. The family must move out for months or more, because the house is not really in a usable state while that many repairs are going on at once.
2. Incrementally rip out and replace old fixtures and rotting boards and such, and generally improve things room by room on an ongoing basis. It's easy to do this while the family is still living in place, and gradually improves things quite a lot.
3. Leave the main body of the house alone for the most part, but build on additions of various sizes. Heck, add a third floor if you want, or a huge garage, or even unattached outbuildings. This is the least intrusive of all into the actual occupants of the existing house, but adds tons more.
What I'm saying is that throughout the 4.0 and 5.0 time period, we were doing #1 off that list above. We'd never done #1 before that period, and I don't intend to ever do that again if I can help it. We tried to make sure that the foundation and general construction would support everything we wanted to do going forward without ever going through that again. Never say never, but it's certainly not a common thing or something to be undertaken lightly.
That said, we plan to do tons of #2 and #3, so no worries. That's basically what everything from 1.0 up through 3.189 is. It's only between 3.189 and 5.0 that we were were in #1 mode, and now we're back to #2 and #3. I think that all of the expansions are currently good examples of #3, and versions 2.0 and 3.0 of the game were both good examples of #2 and #3.
Hope that's a bit clearer.