I definitely agree there should be a text object. There’s several people who have requested this already actually, but I just haven’t gotten around to it:
niedzielski even posted a bounty on the issue, so if nobody else does it I will make sure to get to it soon, and I’ve added it to the Tiled 1.0 milestone.
Supporting bitmap fonts based on tilesets is an interesting idea, though I’m not sure if it’s the easiest approach. Usually the letters are not all the same size, so either tilesets will need to support this (it should be supported eventually anyway) or each letter would need to be its own image. There’s also the fact that you’d need to assign a property to each tile telling Tiled what character it represents. I think there are probably already common ways of dealing with bitmap fonts, and then it would make sense to support that more directly in Tiled. What format is your font in?
In any case bitmap font support is definitely a larger issue than supporting a text object based on system fonts.