I disagree with this view.
I guess most of Imperial population see themselves as planetary population (even country, on balkanized worlds), with only a very small minority (that still amount to millions at least) see themselves as Imperials.
Even while travel seems easy, this is not entirely true, as, aside from being expensive, it’s likely to be restricted in many worlds, mostly those with restrictive governments (and this includes most HiPop ones.
Only those serving (or having served) on Imperial services, or those regularly travelling off planet (and this probably means high society or traders) would think about themselves as Imperials, with most of the population not even caring about the Imperium, either fully ignoring it or seeing it as a remote entity with no effect on their lives. And I believe those two groups rarely merge (to see my view of the Imperial society and culture, see
this old post of mine)
But, as Mike says, that’s for another thread…