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Here is an interesting thread on the matter w/ good links and quotes from Ikuo Tokunaga, Seiko's chief dive watch designer.
http://www.watchfreeks.com/23-seiko/19488-why-does-seiko-use-hardlex-crystals.html
Quote below:
OK, I would explain the meaning more concretely.
The resistance to pressure which SEIKO1000m is virtually asked is at least 2000m or more. High-quality Hardlex of 4mm thickness adopted on 1000m clears this standard. On the other hand, in order to secure the resistance to pressure as same level as that of high-quality Hardlex (4mm) by using Sapphire, the thickness of about 3mm is required. Although both performances are same grade, Sapphire (3mm) is higher about the cost, therefore high-quality Hardlex (4mm) is superior to Sapphire (3mm). -- Incidentally, the thickest Sapphire that SEIKO uses now is less than 3mm. The resistance to pressure of Sapphire (less than 3mm) is inferior to that of high-quality Hardlex (4mm) --
Then, how about the Sapphire of 4mm thickness? Compared with the cost of high-quality Hardlex (4mm), that of Sapphire (4mm) rises very high. However, about the resistance to pressure and the durability of Sapphire (4mm), it exceeds that of high-quality Hardlex (4mm). In order for Sapphire (4mm) to exceed high-quality Hardlex (4mm) also at the point of cost performance, we have needed to reduce the manufacture cost of Sapphire (4mm) further.
In recent years, with producing various kinds of PROSPEX watches, the adoption of Sapphire glass has been promoted, and so many Sapphire glasses of 2mm or more thickness can be manufactured stably. By the improvement of manufacture technology which is related to it, SEIKO has succeeded in reducing the manufacture cost of Sapphire (4mm) to a half of that of 1986. And this time, this Sapphire (4mm) has been carried on new 1000m professional diver’s watch.
One of the key concepts of the SEIKO’s watch making is "The highest cost performance watch in the world." As I mentioned before, SEIKO 1000m professional diver’s watch is one of a few saturation diving specifications watches in the world, and has the highest water-tightness and the air-tightness at a price of about 130,000 yen.
By this time’s model change, user’s cost goes up about 30,000 yen, but I judged that the cost performance of the new model exceeded that of the present model, by considering synthetically the merits, such as the further improvement of resistance to pressure and durability, the materials of the world highest performance, user’s attachment to Sapphire glass, and the other various elements.
At the meaning above, yes, I am confident that Sapphire is better than Hardlex.
Sorry for the long message, but I hope this is helpful for you and other S&C Forumers. Sincerely yours,
Ikuo Tokunaga
I think this is a better quote from the link you posted:
"Seiko makes their own sapphire crystals.
The company found that when sapphire and Hardlex are of equal thickness, sapphire is superior in BOTH impact resistance and scratch resistance.
However, to make sapphire crystals of sufficient thickness for their dive watches (e.g., the same thickness as the Hardlex crystals currently being used), the failure rate (some crystals apparently come out with hidden/microscopic cracks that affect impact resistance and thus need to be discarded) makes them too expensive (in Seiko's opinion) to justify the incremental improvement in performance. Which is why Hardlex is used for all but the most expensive of Seiko's dive watch line (and the MM300 is NOT one of these models, which is why it still has Hardlex.)
This explains why Seiko does routinely use sapphire crystals in many of its mid-priced non-dive (dress, chronograph, etc.) watches. For a non-dive watch, a thinner (and thus cheaper) sapphire crystal can be used since impact resistance is less critical."
Really, there's also something to be said for a good deal =/= to worth the price. I can't vouch for either as the former is based on many factors such as location, and the latter is based on perception and unknown manufacturing and R&D costs. Good luck in your watch hunt!
If you by some chance meant will the 8L35 be replaced by something newer soon, the SBDX017 recently came out with it so most would likely lean toward no. And like other movements, it has seen small changes or upgrades over the years, i.e. the A, B, etc. designations, for which there generally hasn't been a release or change log.