Well, the basic idea was to have some kind of normal development, but not by implementing things slowly, but by making certain modern things so hard to build that the world has to develop more before they come into place. Apparently, it hasn't exactly the intended effect.
Also other things were intended to modernise. For example, guns have been on the list from day 1. However, if we would allow guns now, whereby one shot can be killing, this would have a devastating effect on the game. Hence, we need weaker weapons, hence we get more historical again.
It's very hard to make something that develops naturally, reaches a modern state in a reasonable time, and keeps a good game balance.
Btw, part of this is also due to the main example for the game - our lego game

... Here we had cars (more common than in Cantr), but at the same time swords were an important weapon. Although guns and rocketry was more important.
In fact, I would really prefer to work out the problems with modernization and then make the game more consistent with a modern environment. With ships, for example, my idea was to wait for the slow sailors to discover the other sea a bit and have them mapping things, and then allow heavier, modern ships to be build. Similar to what I had in mind with the weapons.
Also other ideas that I have in mind and should be fairly simple to implement - radio, trains, etc. - would be really cool, and sticking to a medievel level would disallow this.
Helicopters also have been implemented from day 1 - they are just not allowed to be produced yet. Rocketry would be really interesting if we could implement it (and I don't see why not). So, in other words, I'd like to keep the game as it is, but gradually work on improving both what we have and more modern items.
But it seems there are few that agree ....