Nothing stopping the removal of the header tank, and capping the F&E pipe to make it a sealed system.
A heating only boiler is equally likely to run a sealed primary these days as a system boiler. As to whether its worth going for the straight swap depends on what problems you have with the existing setup. If it works well as a vented system (i.e. no pumping over, no need for constant bleeding, no corrosion problems, no airlock problems on filling etc), then no problem sticking with it. If however there are problems, many can be made to go away with a conversion to sealed operation.
If you hook it up to a same brand unvented cylinder then its straight forward. If you want to integrate a different type with standard mains voltage valves etc, then you need an extra module IIRC.