Greetings! It should definitely be possible to set up at least 10.5, using the same emulator template and settings as apply for 10.4 environments, so long as you are using 10.5 installation media intended for PowerPC Macs (I believe that 10.4 and 10.5 were both released in PowerPC and Intel x86 versions)
Tthe Emaculation forums confirm that qemu-system-ppc (which we use for emulating PowerPC Mac OS versions above SheepShaver’s 9.0.4 limit) should be compatible up to that point: Running Qemu-system-ppc with Mac OS/OSX guests in macOS [E-Maculation wiki]
As far as I am aware we are not currently able to address any OSX versions from 10.6 or higher in EaaSI, as those versions require 1) a far more complex set of QEMU options and 2) a separate/custom piece of firmware not included in QEMU by default to work at all (I’ve tried to follow e.g. these instructions before in a local version of QEMU, to limited success), and there is not currently an emulator image or hardware template available to map all that to EaaS. (See @rafaelgieschke’s same answer re: other QEMU versions as to the difficulties of EaaS’ hard-coded emulator support: QEMU - users requesting versions later than 3.1 - #3 by rafaelgieschke)