Quality of the rendering and, in particular, position of labels should be top notch. There has been lots of work done on rendering in this library with lots of attention to details. When compared to libosmscout, Mapnik had much more developer-hours poured into it with the focus on one aspect of the function - rendering.

The stylesheet I was thinking to start with is https://github.com/mapbox/osm-bright . Maybe there are better styles out there that should be considered as a starting point. If so, let me know (ASAP).

When I manage to get stylesheet fully ported (there are several steps involved), it would be possible to engage end-users into design of the map styles using tools developed for Mapnik. Again, eco-system of Mapnik is much bigger allowing us to reap benefits from it.

As for speed of rendering, this is hard to judge right now. With a crippled style I was using it was very fast, but let's see it later.

There will probably be drawbacks too. In particular, right now, the data files (SQLite database) for feeding Mapnik is 2-3 times larger than libosmscout import. But that datafile includes all traffic lights and probably some other not so important information. For now, it was important to see that its actually possible. Let's see how well would it work out.