You need to define which old hardware to support. There must be a limit, otherwise Slitaz will become another dead distro, as many others.
For me the reason behind installing Slitaz on an old hardare, was to be able to run new and modern applications on that hardware. Otherwise Windows98 or XP can still be used without any problem.
IMHO, Slitaz must follow new technologies and instead old hardware to focus on ARM and MIPS. This is the way where the technology is moving. A 25$ RaspberryPI will be more tempting than any old hardware.
Wayland is the missing part of Linux. Is adding coherence and unity in a fragmented X world. X was the part who blocked main developers to build native Linux applications. In fact you can number on one hand native X applications.
So, IMHO, Slitaz must go to support ARM, MIPS and slowly integrate Wayland protocol.