Having operated them in the past, drum scanners were bitchy, painfully slow, required disgusting amounts of service and quite extraordinary amounts of consumables (Mylar sheets, fluid, cleaner, cleaning wipes and the odd drum and lamp ever so often). Nobody doing a run-of-the-mill scan service can still do that profitably on a drum scanner, and the few individuals still making money out of them have tweaked their scanners to perfection, and probably would not be inclined to switch to a new scanner built to meet a much lower price point...

Currently the market is that saturated with old pro scanners that there is no profit in any new high end scanner development. Whenever there will be enough demand to start high end scanner building again, it will be in low numbers, and will probably take a entirely different direction - more like a 2D Imacon or those micro-movement enhanced medium format backs.

A high quality macro lens, FF or APS-C sensor and a piezo base for micro stepping the sensor to multisample at a finer than raster pitch should today be capable of delivering above 100MP scans at pro digital camera quality, using current off-the-shelf components rather than anything proprietary or not made any more - which is essential if the thing must be affordable enough for enthusiasts and archivars rather than the advertising industry, and has to be made by the ten rather than the thousand.