What I can imagine freaking people out looking at your code is not knowing what, if anything, is atomic or otherwise in a transaction. Presumably that's well-defined by the ASDF operations and whatever multi-threaded solution you're using in Lisp along with the Lisp runtime guarantees, like presumably (I haven't looked) if you compile and load a package through ASDF it will do it all at once (but for each thread?) and you won't get in a state where one thread has a reference to both an old and a new function in the package. You might still have an issue where one thread expects a database schema that no longer applies because you've updated the schema and the mapping code was updated by the package reload but this thread hasn't had that happen yet...

For your web system, are you guaranteeing that if any subsequent requests come in, they wait for the current request to completely finish before being processed? If so, at least there's no obvious bug and the recompile only happens once, but that will turn people away when we're in a many-CPU age. So it's really not that different from the CGI model that PHP has used so successfully. FTP a new copy of the PHP file onto the server, presto, all new requests use that code and you didn't have to restart anything.