That's the nature of progress. It's not like multi-layer XL is any more compatible. I just want the standard to include single layer as well.
I don't know what Sony's motives are, but I'm all for more capacity, particularly when it's a minor update to an existing standard.
I don't like DL. Expensive, and even though I have no real data, I'd assume also less reliable due to the layer bonding process.
Another media type is no different from the 74/80min CD situation, and still better than DVD-R vs DVD+R.
I think it was more expensive because it's a more radical change of technology. But I rather have 25GB discs than 15GB, even if those 15GB are cheaper initially.
Again, XL is incompatible, its a new brand. So why sell a disc that is of lower capacity then the max capacity of the more widely support version. It doesn't make sense. XL is going to be a much more expensive disc. It's easy to sell it for much more because of the doubled up capacity. But selling a 32GB version for more then a 50GB disc, just means only people with durability concerns that might not be grounded in reality would buy the 32GB versions. XL is never going to supplant and because of the use case that is pushing the technology really coexist with BD SL and DL.
The Motives matter because it will explain why there isn't going to be wide spread adoption. Sony developed BD from technology that they had been selling for years in the Japanese and really high end surveillance market. As 720p and 1080p and color capturing goes up, Sony needs the capacity to increase. When they finally published BD as a standard suite, they started using that for these businesses. So to keep up, they need to sell more upgrades. Now they have gotten more parties involved displacing the cost and eating some of the overhead, where it can have more uses. But in its heart XL is just a write once PVR media. For everyone else its an addon to BD and BD E. You don't add on by offering a size smaller then what you are already offering. And again, since these are a different technology created for an extended use case its never going to see the production that BD E has gotten, and honestly even that is being held back, to keep the media more expensive so that people don't use it to write ripped and or downloaded movies to it.
As for DL, I get it. Specially back in the old days before software was smart about it there were dozens of DL writing issues. As for the bonding. These are always supposed to last a century, but even if not that, decades. I don't know what your writing, but chances are decades from now 90-99% of that information will be little use for you.
As for media deviation. It's not anything like the two. CD 74-80 was pretty much exactly the same disc. If you took a plextor that allowed over writing, you could get a disc that held about 750MB, whether you used a 650 or 700MB disc. 700MB basically as part of its digital label told software that you could write more to it, nothing else. DVD-R and DVD+R was completely different, because it only affected the writer you choose and not where the results could be read. Slightly different burning algorithms and writable reflective materials. But the end result was a DVD that if you wrote video could be read in any DVD player and Data in any ROM. XL is closer to DVD-RAM then anything else, which if you remember the caddy system was designed for exactly like what I am talking about now direct write PVR. Guess what the media stayed expensive, pretty much died out, and then they add it to other writers for legacy reasons more then anything.
Its going to be more expensive because they want it to be. They are not going to go DVD media like crazy with it and by keeping the media expensive they can also keep supporting hardware expensive. Sony owns all the important patents for this, they won't license a manufacturer to produce media or drives where it will push down the price. This is going to be a competition less product, aimed a particular use cases, and not as a general use product.