Hi,
unfortunately there is no update towards DSM 4.3 neither to DSM 5.x for my old DS-108j available. Nevertheless I managed to install the Baikal package on my DSM 4.0-2228.
On the other side the author of the Baikal installation package - many thanks to Eric for his great job - limited the installation to DSM 4.2-3160 (or newer).
I solved this dilemma by - sorry for this! - hacking the installation packeg with an hex editor and replaced the firmware entry according to my needs.
I can confirm, that the Baikal caRDdav server (with sqlite) is running without any problems on my DSM 4.0-2228. I deactivated the caLdav server, because I'm using the Synology 'build-in' caldav server.
Maybe this information is of use.
Br
Uwe