Despite their relative liquidity, I don't really touch 4L .com's because their initial purchase price is high .. and quite frankly .. unless you're going to do outbound, they will likely take a while for end users to find you.
But that actually brings me to the next more important point. Which is that I think the future will see "smarter" prices.
Meaning that the value will have a wider range depending on the actual letters and placement of said letters.
For instance if you listen to
@DomainSherpa Reviews, you'll notice that
@Domain Shane and
@MediaOptions both tend to prefer 4L's ending in the letter "C" .. because it is essentially a 3L followed by "corporation" or "company" (which means a higher number of potential end users). On the other end, 4L's ending with "O" aren't so valuable because a lot of end users ending with "O" are "Organizations" .. which means that instead of grabbing the 4L, they'd likely grab the 3L in .org .. essentially lowering the number of potential end users and lower the "demand" side of "supply and demand".
The Chinese market is also getting smarter in that instead of just blindly buying everything that doesn't have "A E I O U V", they will likely move to value letters based on actual end user letters in actually use by real companies. Demand there was also artificially increased on Chinese Premium (Chips) liquid domains because of their weird p2p loan system that used liquid domains as collateral leading to a bubble effect.
Also .. as super premium one dictionary word .com's become ever more rare and more expensive, pronounceable 4L's that pass the "radio test" most certainly will see demand increase from new companies with serious funding in need of a serious brand name, as 3L's and good single words move into the 6 figure range (end user price).
So in the end I think from this point forward you'll see a wider range in pricing for 4L .. while some will likely go up significantly ... other will see softening and go down in value (although I don't think the bad ones will go down all that much .. they will still have some liquidity as there always seems to be some "investors" who buy stuff that don't make any sense to me because the chance an end user would ever use a domain like "KYWQ" are way too low to justify holding .. lol)