Mark pretty well sums it up... There are issues with the frequency response that arise directly because of the non-inductive nature of this driver (Le is 27 uH):
As you can see, the frequency response - while extended to 12 kHz (without a whizzer) - does rise 12 dB from 500 Hz to 5 kHz.
Additionally, the sensitivity is 86 dB in the low end, which kills it as an option for most FR guys, since they are overwhelmingly the "sound of one Watt clapping" type of people (seriously, full-range fans willing to use more than 1-2W of power are a slim segment of the full-range market).
The point here is that XBL doesn't force you to weird inductance, or high inductance. You can do low inductance, and you can do ultra-low. And that each driver tends to be designed for specific design goals which are not often in the interest of the DIY hobbyist.
Realize that most of the offerings from the larger companies are cast-offs from OEM designs. An OEM commissions a factory to design and build a certain product. They do so, and build it for a few few years until the OEM changes the model.
The factory typically takes that design, changes it cosmetically (different basket, different coating on the cone) and then places it into their "stock offerings" catalog. So what you end up with is a lot of other people's solutions, not really your own. Which is also why OEMs tend to just get new designs done; if you're going to build 500+ drivers, it makes economic sense to just do your own from scratch.
Having experience in the DIY and OEM world, I can tell you that the former is a lot harder to deal with because of the demand for the best and the greatest without realizing that it comes with problems which are often diametrically opposed to each other, and the latter is hard because of pricing. Pricing is easier to negotiate; pet theories or demands or ignorance - especially in terms of audio and sonics - is a lot harder to overcome.
And of course pricing is seriously difficult with DIYers, too... You end up with OEM, big-volume and annual commitment quotes being reported/represented as individual, retail prices (like happened in this thread), and then the DIYer getting pissed because the actual retail price is just outrageous and gouging. Never mind that the DIYer will buy one, two, or maybe 4 units. And the distributor and small OEM - who needs to make a profit as well - will buy a few hundred each month. Pretty simple to see who gets the price love there!
I'm sure if the market manifests itself some DIY supplier will take up the challenge, and would be willing to make a driver like this. It won't be cheap, and there will be - by necessity - a significant minimum buy of quantity (good luck getting less than a few hundred speakers made at a time). And there's tooling costs involved, too... All told, rolling out a new driver can run a DIY supplier well in excess of $40,000 per model. That's a lot of sales of a $50 driver to just break even!
And understand that a lot of the problems with the DIY market getting castoffs and being treated as second-tier is because the DIY community demands it. They will take a great driver and completely destroy it because of a perceived fault; even if that fault was incorrectly measured, observed, or flat out wrong.
Sure, driver A may have slightly more THD+N than driver B, but driver A has lower power compression, lower THD+N in dynamic situations, better dynamic stability, easier use in a variety of boxes, more stable product supply. But in the DIYers mind, that difference between 1.5% THD+N for driver B and 2% THD+N for driver A- a totally inaudible difference - is simply case-closed! Driver A must be better because it just is... Missing the forest because of staring at a single tree.
Bottom line: there are tradeoffs everywhere, and usually demanding the best of everything means you end up with the worst amalgamation you've ever seen!
Keep in mind that John Dunlavy did some amazing speakers with just $10 tweeters, $12 woofers, and iron core inductors...
It's the execution of the whole, not the individual parts that matter! That holds true for drivers, too... Great technologies (like I think XBL is) are good blocks, but still need to be tempered by the overall performance and goals of the execution and the budget and production requirements.