So after almost 7 years, this finally happened:
Strangely enough, it doesn't really feel huge because it's so stretched in time. Look, first you become a permanent resident, and there isn't much to celebrate because for everyone concerned you are still a foreign citizen. Same queue at the airport arrivals, no voting even in local elections, no ID that doesn't scream 'immigrant'. Well, it grants you right to be employed without any formal restrictions on the hiring process, but my previous visa allowed me into the same labour market position as well. As a permanent resident, you can also apply for various state benefits such as tax credits (apparently) or council housing, but again I was lucky to have never needed that, and neither do I now.
This status does offer security though so you stop worrying about your visa not getting extended next time (not very likely provided you comply with the rules) or paying ever-growing fees (this is big actually), but that's about it. Something you can certainly feel, but still nothing to write home about really. This is where you start hesitating whether to celebrate now or to wait for the next, more prominent milestone. And indeed there is one coming, the problem is it is not the last in the line either.
A year after becoming a permanent resident you can apply for citizenship, but then again you don't have a single 'this is it' day where you can draw a line and throw a party. First you get informed that your application has been successful. Hurray, but technically that doesn't mean anything yet because you have to attend a ceremony and receive your certificate. Which doesn't happen too soon. In my case, for example, it took about a month because there are only so many days a month the council does ceremonies, and I had travelling plans as well (as after you become a citizen, you can no longer go abroad with your old documents).
When you finally attend said ceremony, it still isn't the end of it, because you don't have a passport. You only need it to travel abroad, but doing so effortlessly is one of the great formal benefits of naturalisation, so you usually apply straight away... and wait again because in Britain you have to be interviewed in order to get your first passport, and you got it right, that usually cannot be booked too soon. The point of the interview is to prevent identity theft, which in case of a naturalised non-EU immigrant like myself seems redundant as all the data including biometrics has already been submitted many times before that, but the rules are still the same.
Finally, a day comes when you receive your passport - yay! - but at this point that is something you, in a way, take for granted and there is no that feel of genuine excitement (still feels incredible of course, but you kind of have crossed the finish line earlier, right?)
Another predictable, yet still funny thing is that everyday life-wise it doesn't really change much. People who don't like you because you are a foreigner (not that I can personally complain too much about that though, but nevertheless) couldn't care less about whether you have a passport or don't, as a rule. Similarly, people who used to like you before aren't going to like you even more because of that either. And more importantly, you are still the same person. You still get into awkward situations a bit more often than you'd honestly prefer. Your accent is still a dead giveaway. You still have had a very different childhood comparing to any of your British peers, and that's even regardless of the social class. I can go on and on.
Yet I've still been feeling an urge to write this, mostly because I realise this has been one of the biggest projects I attempted in my life so far, and it has been successful. I am also now holding a far less idealistic view about the UK comparing to what I imagined it to be when I fist got an idea about moving here, but at the same time I am feeling a lot more involved and accepted that I dared to hope for which amazes me more than ever, and for that, I am grateful. My admiration for Britain is still there, but is now backed by different, less naive and postcard-worthy matters - which, unlike the latter ones, are less prone to being shattered by brutal reality I am much more aware of as well.
10/10, would do again.