06-11-15: Larryi
There are not that many "modern" horn drivers that even come close to comparing with some very old designs, apart from some attempts at exactly replicating those old horn drivers (the Japanese G.I.P. drivers, for example). Those modern, non-replica horn drivers that are really good are also terribly expensive, such as ALE drivers (a set of drivers cost more than a house). What else do folks put up as examples of modern compression/horn drivers that can compete with the best old stuff: Avantgarde?
Some of the older, sought after driver designs are, as you point out, quite (i.e. insanely) expensive, so for most who don't intend to rip their back pockets to shreds cheaper alternatives are called for. Here the modern designs (or simply new, rehashed dittos) seem the better option compared to their older siblings, if nothing else simply by virtue of being new and at least comparable in quality. It's a shame AlNiCo magnets are not more prevalent in newer designs, but price is likely a factor.
Those über-design units of the past are certainly something to strive for, which can be seen with drivers like the B&C DCM50 (inspired I believe, though a "convetional" design, by the RCA 1428 field coil unit) - at an affordable price. Some find it's one of the best midrange compression drivers around. Mr. Weiss of OMA and his Cogent field coil units would be copied/inspired designs as well, but should one be able to buy them I gather they'd be.. expensive.
Modern cross-overs are, if not necessarily by design then largely much better due to the advancement in materials used.