There isn't much to discuss. If you use sid(uction) it gets complicated if you wait too long.
And recently we had a thread in the software section, where the already completed perl transition, which however was ommitted by the user, prevented further d-u_s. It was solvable, but it was an unnecessary hassle for all parties.
As to kmail:
I once and for all solved mail problems by runing exim4 localy and whichever IMAP-mail-client I like and when I like it. I really hated it being dependent on some POS software.
kmail isn't one of the clients I use, but currently, tested 5 minutes ago, I could install it on my system without removing anything.
Which proves "it gets complicated over time, when you do not d-u".