game is all about alts. It would not prevent anyone from playing the game, it would prevent people from playing with a certain character until a certain pre-requisite is met.
Nah, game isn't about alts, it's about tent decoration. See what I did there?
The problem with a statement like that is not only that it is highly debatable imo, but also that - since you are not arguing for a feature that prevents people from playing the game in itself - the whole validity of your suggestion as a reasonable feature depends on that assumption being true, otherwise it would act as a symbolical off-switch again, at least for part of your playerbase (and for what it's worth most likely the vast majority of new players). In other words, if you accept the prohibitve nature of such a system as terrible design, your counterargument to that is "you're playing the game wrong".
However let's cast that aside for a moment and address a few more concrete points. A few pieces of information as a baseline: technically I'm part of a player faction. Two people, two chars, no alts. Surprisingly, depending on what you think our ambitions are, we're actually doing pretty good. Rather nonsurprisingly I can tell you right now that ambitions definitely don't involve anything that require alts for validity.
So let's imagine I get captured.
How is my faction going to be notified? Hopefully that is not expected from me, because not everyone is using IRC, I surely won't have a radio while being imprisoned and PM seems like a great idea to just drag the situation out further. In any case smaller factions that could add diversity are going to take it up the ass, simply because a lot less players would be online to receive a notification and act upon it.
So let's say there's an attempt to bust me out, what's my role in this? Running, I'd expect, but since, because of the outlined communication issues, there's a non-zero chance I don't know when that would happen, I'd have to idle around in a cell in the meantime, doing exactly nothing. Of course I could try to chat it up with my guards relying on my charme to get me out of that mess, but chances are they weren't too talkative when they opened fire to begin with. Also, the whole busting out scenario is now kind of off the table, so smaller factions that could add diversity are going to take it even deeper.
Last option: ransom. Where would it be delivered? Since you probably wouldn't trade with anyone without seeing the goods, there's basically one place left to make the exchange. So where I was careless (or what ever circumstances led to my captivity), my teammate(s) are now forced into potentially repeating that mistake. Not to mention that one payment of 24k may not be a big deal, but it would potentially add up. Smaller factions ... you get the idea.
Obviously there's workarounds for those problems, but off the top of my hat I can't think of any that not only don't involve alts, but also almost trivialize the issue. Alts for base creation that just add pvp builds as friends, so no one of your targeted audience is even viable for capturing as has already been mentioned, for example. Or simply ignoring the situation for 24 hours, if the alt is released after that anyways. And possibly not taking part in any action where that alt could see use, I'd imagine.
Now what are the implications here? I'd assume the impact on your target player base is minimal at best. From my perspective occupied towns are dangerous to begin with. Which is fine. Once I drop there's a reasonable chance I get my ass bursted and sent to respawn. Now change "getting shot in two seconds" to "getting pummeled for what seems like ages by a HH troll that doesn't do too much damage (we don't want to kill the hostage, after all)" and "1 minute respawn and loss of whatever I carried" to "out cold for a day". In other words, since I chose to play a single character, there is absolutely no viable scenario in which I'd ever visit one of those locations again, effectively turning content associated with high risk into practically near inaccessible content. If that sounds like too much whine, imagine I'd flip the tables and propose no access to guarded towns for alts. Would be ridiculous, wouldn't it?
One of the few things I like about this game is how people who enjoy the RPG/social aspects of it can blend together with players more interested in interfaction conflict. In fact I think it's its redeeming quality and while I'm certainly not a fan of some of the recent changes, it's a tough job to balance these two groups against each other. What doesn't help, however, is pretending one group doesn't exist or flatout telling them they're playing the wrong game. Which may even seem that way from your point of view, but I am under the impression that the majority of new players I meet (and it's been a few) actually don't initially plan on developing multiple personalities, but often do so out of perceived necessity - or simply quit. Bottom line is, while I am highly in favor of almost anything that adds realism and/or makes the game
actually harsh, right now I fail to see how such a feature would do anything but being a mild annoyance at best for one part of the player base while severly fucking the other.
On a personal note, yes, if such a thing even exists, I am probably playing the game wrong. However that usually leads to me trying to assist new players I meet by helping them out with some gear/hides take them along to get their feet wet by shooting at Brahmin in RT or stuff like that. If I were playing the game "correctly", chances are I'd advise them to make alts for bursting and looting in guarded towns, imagine how much fun that would be for all involved. Generally diversity is not something you want to get rid off.