Hello Everybody,
Thanks for your interest for this subject. Finally , I decided for user temporary dbs, either RDDB or IMDB depending of RAM amount I can afford, as I really saw with sysmon a big number of log access avoided and ulc flushes skipped. I fortunately found two appnames which will allow me to avoid managing several hundreds of logins.
I can understand risks by putting system tempdb as imdb , perhaps the ability to bind a group (here users group) , added to login and application name, to user tempdb (or tempdbs group) will make easier unsing this feature.