Can we expect new GPUs from the Titan series to be out soon? like a smaller one in performance / price??? around like $600-$750, or this is only a One Titan card??

Titan is a series of cards like the 500/600 series, the next series of cards (likely named the 700 series, because hey, I can detect patterns) will instead come out sometime in the future between now and never (I don't like making risky statements about my speculation)

I doubt that the geforce titan are chips that 'failed' in DP 100% loads as you stated.  You can turn on DP in Nvidia Control Panel in the titan. - If these chips were failed in DP then such an option would not be available.
 
I'm guessing now that Nvidia fulfilled its contract with the HPC market - they got chips left over.... only customers left are us consumers.

Titan isn't part of a series-- sure, EVGA calls it that for the forum name, but they did the same with the chipsets for their dual-socket boards, yet they don't make other SKU's.
 
Titan is one random circumstance that won't have a successor as nVidia took advantage of a void left since AMD isn't there to compete or control the price.  If there was competition, i.e. an "HD8970", then the GeForce GK110 wouldn't be priced at $999 and wouldn't be called a "Titan", it would be $499 and called GTX685 or GTX780.  Then only yes, there will be cheaper models because AMD would also be making cheaper models.  But all rumors suggest AMD is postponing HD8000 deliberately out to the end of the year, and since GTX600 is able to hold off HD7000, there was no reason for Titan to exist in the first place except to act as a cash cow.  
 

vacaloca 
Actually, my K20 has 1 less SMX enabled compared to the Titan, not to mention the clock on the Titan is actually faster... I'm not totally convinced that's the reason.

How about product lifespan?  
 
Apart from competition, Intel doesn't debut faster processors, we know we can overclock them faster, but none of us keep or use them as long as Intel's warranty; which is a three year non-stop 24/7 absolute guarantee.  In terms of cyclical loading, the whole reason we can overclock them so well is because they were designed for endurance at a lower stock clock.  
 
It is much more likely that these Titans didn't pass whatever nVidia's stringent pre-test quantification for a K20X to last as long as they normally warrant in terms of lifespan and mission critical use.  The 105MHz extra base clock is just pathetic, they might as well have left it alone, except Titan would have come off as no faster than any factory overclocked GTX680.
 
nVidia didn't just suddenly realize there was a market for GeForce GK110; it was always there, but it was thin enough to not address unless those demanding could pay for it.  A bunch of things worked out in their favor:  

• My guess is that these Titan GK110's collected as dies that didn't qualify as K20X but still functioned until nVidia had enough to turn a profit.  
• Considering that Titan has a gimped power system unlike other consumer graphics cards that limits input wattage, likely originally from K20X since that market gives a big darn for power consumption, it doesn't look like nVidia put much extra work into the PCB circuitry.
• Most importantly, the lack of competition that allowed nVidia to assign an MSRP as high as $999 to turn a profit of those leftovers and not fully unlock the capability of Titan since AMD has nothing to keep nVidia honest-- it all just happened to work out, none of this was planned from the beginning.