There have been microblogging apps before here, they just tend not to be received well. I think the latest is d.buzz, but there have been a few others over the last 5 years (old chain included).
In regards to scaling (due to Resource Credits) it doesn't work, but with resource credit delegation coming, combined with the ability to create "hotseats" for them, it is very much possible - but it requires some additional changes (next HF) and different kinds of apps to be built.