That is an interesting idea.
I am not sure that it would be any better / less complex though than just changing the entire system over to 24 volts.
SES Flexcharge makes a taper charger and I use it in "some" 48 volt AGM systems, but it isn't Li compatible.
There are some other solutions for dealing with small (sub 1000 watt) mobile arrays that I use but they require dividing the array into 2 sections and using 2 controllers. It works but not without some trade offs.