After the "gun" type burner was developed in the early 50's, it looks like technology pretty much stagnated in oil heat. The highest efficiency I've seen in an oil furnace is around 85%, while gas furnaces are all the way up to 98%. Oil furnaces are still using huge 8 inch flue pipes and natural-draft.
Yea, there are some furnaces out there with variable speed blowers, and you can perks get solid-state igniters on new units, but nothing like the technology you see in gas furnaces lately. Oil furnaces are still using the "drum" style heat exchangers that gas furnace builders abandoned in the seventies. Oil furnaces still burn with bright yellow flames. Hasn't anyone designed an oil furnace that can fully vaporize the fuel and deliver a "bluer" more efficient flame? how about multi-core heat exchangers like gas furnaces do, or secondary, condesing heat exchangers to extract more heat? Induced draft? Variable speed burners? stuff like that.
I hear all sorts of hype of "replace your old furnace with a new high efficiency one" but the thing is, it looks like things have been pretty much the same in oil heating for at least 30 years or so, so why? Yea, fuel oil is comparatively high now and people are replacing them, but it wasn't only 8-10 years ago, and a lot of people were happy with them. Why weren't companies investing in R&D on them?
I had an HVAC company come out and spec a new heat pump, and he spec'ed in a new oil furnace with it. The furnace he spec'ed looks pretty much identical in internal design to the functioning one I have. (I want him to just put the heat pump on top of the existing furnace) Unlike in gas furnaces or heat pumps, where one could in fact replace equipment 10-20years old and get a significant efficiency gain, it looks like there is no reason to replace an old, but perfectly functioning oil furnace unless it suffers a major malfunction.