Does not holivara for the sake, but purely for informational purposes.
There is a site with a very large number of visitors (~50.000/day according to GA). The website now consists of a large number of completely unrelated component, running on different engines within their subdomains. To write crutches for the mutual linking of all engines and authorization profile is not desirable, and ready-made solutions for these purposes was found.
In this connection it was proposed to use as the main platform for Joomla+JFusion where to build (like there is modules) the whole zoo engines and resources, thus making a single authorization.
Question: how reasonable is it? How safe and easy to maintain? Well, not if it will eat a lot of resources? Ask these questions, because the practical experience of support of sites on Joomla does not have, and opinions on the Internet about Joomla is very different. Main goal is to tie together the whole zoo.