It's not successful ever due to the low population that Blockland actually has. If anybody is playing the game at all, they're either in a TDM or building by themselves.
You only really have the option between small children and the people who come by to try to wreck the server.
This is a rather negative comment and isn't necesarry, as it's pure opinion.
Roleplay servers can get lots of players and can be popular. It is not a fact that this server will not gain players.
I personally really like the idea, and I also like the fact that you've taken to setting out proper roleplay rules.
I have a couple of niggling problems with the rules you've set out so far, but nothing major.
I personally believe you should allow OOC chat, but in the medium of, say, Team Chat.
It can be very frustrating if there is an actual server-sided problem, or administrative query/problem that someone wants to bring up, but can't due to the lack of OOC. Not everyone has RTB, and not everyone responds very well, so I wouldn't rely on it as a means of talking to the players OOC.
You'll also very much find (unless you have rules on joining) that a number of people joining the server will immediately start by typing "hello" and other such stuff, like questions about the server. Telling them there is a medium for OOC chat can be very helpful.
I'm not keen on the baby idea. I do think it is necesarry due to the setting of the roleplay and all, but I'm not sure about the whole "everyone is a baby if they join after this time" thing. It seems very much that the roleplay could go awry. You may also find you attract a number of immature roleplayers used to Family Rps and being children. A number of them like to pretend to be a child, but then constantly talk and get in the way and try to revolve the roleplay around them. Which just isn't realistic or helpful.
I think the baby thing should be allowed, but perhaps not enforced to all, and perhaps not made in such a way that everyone can be a baby/child. If you're going for a serious roleplay, it's a very difficult position for someone without much patience or common sense to fulfil.
I'm not sure on the Medieval Text Mod.
Since this is leaving the Stone Age, I don't think Medieval text quite works. I don't know what sort of changes it makes, but if it changes things to like "Doth/Thou/Verily/Thy", then it shouldn't be in there.
It's just not realistic.
I know you want actual language, but it is probably better to just stick to normal english for a mixture of both clarity and realism. Unless you want to have either an unrealistic language or an impossible to understand language.
I do however question what sort of constructions you are going to have.
I understand the point of being a nomadic tribe that is slowly settling down, but if you want realism and playability you'll need a couple of things.
As Nomads you'd likely have some equipment with you. Some form of shelter. You'd obviously not just stay in the frozen Tundra in the open overnight.
And you'd likely have some form of livestock or roaming animal you hunt/use.
You may also find that players often need a little bit of backbone to get them going.
A tent or two, or a campfire or something can really set a roleplay in motion.
If you were to start a roleplay up in a small box with nothing in it, you can't do anything. If you set a roleplay up in a big empty box, you still can't do anything in it.
You'll likely want players to slowly start building stuff, but that's going to take some push to begin with.
And if you're nomadic and wandering about, I worry how far you'll end up from spawn, and if any thing is built far away and you save, you might not find it again when you re-load.
I think the server could be quite interesting and assuming you get proper people joining you could get a very clever roleplay.
I do have those worries about some of your rules and how you'll organise the roleplay, but I do think you'll probably find some way to set it up.
Since it's nomadic, I can't really ask for pictures since it would be blank slate.
I would suggest at the moment that you edit the Title to be something like "The Dawn - (Blockland Roleplay)".
So that, since it is in Off Topic at the moment, people know what it is.
And also so that it gets picked up by a mod who can move it to General Discussion later.