I think you'll be able to do it all, just as you're now. Just that it won't be as efficient, let's for example say you were to run a car wash all by yourself, you would be able to do all the steps required for the task, maybe be good in some and not so good in the rest, but someone who's focused on a specific task, would do it much faster and better than you could. At the end, both you and the specialist are able to accomplish the task, with different results, what may have took you 20 minutes, he did it in 10.
No one is impeding you from building your own huge building, since the devs have mentioned unlimited plots it's thing, how hard it's gonna be to get plots it's another.Obviously a team of people working together is gonna have bigger chances at making a huge city, than a solo player, but that's just how teamwork works.
Good buildings are meant to catch the spotlight, no need for you to get in a city for it to be seen, or get with a group of people, take the hand @30nstillgaming made for example, he did it solo, nowhere near a city, and it caught some attention, because it was nicely done. People and devs liked it. It was a solo project and it got the spotlight.
I think mastering everything should be an option, it should, but how hard it will be to earn skill points, how many skill points would be needed to do it is the key. Take for example getting a Major at a university, you could go and do 5 years to get your engineering major, then go for 5 more to get business, 5 more for economics, what you did in 15 years, 3 different people could do in 5 years each and work together to benefit from it.
What you take to be able to do everything to the most efficient way possible, should be exponentially longer, than the combined time of a group of specialized individuals mastering their craft, if not, there wouldn't be a sense in specialization.
It should be an option, but not something so easy, that everyone ends up mastering everything and not relying upon others. What mastering everything would mean is getting players like you to enjoy the game, which it should, but it should be handled properly as to not weaken some other aspects of the game, as it's communities, classes, and in general the MMO feeling of it.
There's actual games where you're bound to one class, in boundless (Pun intended) it seems to be free, which limits and roadblocks put in motion, to limit choices, so you think through them.