Okay, recently in many battle threads I have seen people claiming that since his death at the hands of Drax, Thanos has become
an embodiment of death and has been imbued with powers of death itself, rather than, you know, just being dead.

Personally I think this is just fan-fiction, so can anyone present some evidence to support one theory or the other?

This is the only evidence of that. Thanos standing at Deaths side after his death.
I don't think he's been seen doing anything but watching. Take it as you will.

Personally, I see two ghosts standing together... but people have turned that into a freaking tabloid show...

I have seen that Death Thanos can beat PC Darkseid...

But are there any feats because if they are not how could anyone even know....

 We will see, as far as I understand it Thanos has not been seen in person since his death
 
but rumors have it that Thanos is back
 
If the modern amped up Surfer actually can give the new Titan man a fight, maybe even knock the Titan on his ass then we know Thanos has got nothing more. He gained nothing from Ms Death, if the Silver Surfer can challenge him then he's no more powerful than he ever was before Drax owned him. 
However if he returns, starts wrecking up Galaxies and absolutely stomps and mutilates Surfer. Then Thanos has got one serious power up and there's something very scary going on

"  We will see, as far as I understand it Thanos has not been seen in person since his death but rumors have it that Thanos is back  If the modern amped up Surfer actually can give the new Titan man a fight, maybe even knock the Titan on his ass then we know Thanos has got nothing more. He gained nothing from Ms Death, if the Silver Surfer can challenge him then he's no more powerful than he ever was before Drax owned him.  However if he returns, starts wrecking up Galaxies and absolutely stomps and mutilates Surfer. Then Thanos has got one serious power up and there's something very scary going on "

not that ive ever seen. traveling realms and assuming a new nature doesnt really make one an abstract.
id ask those who claim such a thing to provide actual concrete evidence to support the claim and id be 
interested in seeing this myself.

 Its difficult to know where to rank Thanos, 
before his death by the kryptonite Drax I would have classed him as a low/mid-level Skyfather 
above him IMO rank the true Skyfathers like Odin, Tyrant, Surtur, Yuga Khan, Archangels, Shazam etc
 
Way above Skyfather rank the cosmic abstract concepts
 
You have Chaos in Marvel 
Death of The Endless
Ultimate Judgment like the LT and to a lesser extent DC's Spectre 
 Celestials, Imperiex and the Quantum Mechianics


The Devourer - Galactus 
and he comes with his instruments like his planet eating machine and his hearlds like Stardust and Surfer

Mistress Death also has an instrument, its the ruthless brainiac Thanos 
and she considers this Deviant-Eternal her personal champion. 
They had a weird loveyou-hateyou obsessive relationship that began from his young age
and led to the Titan going a quest for power and conducting an orgy of murder and death during many times of his life/lives, even wiping out his homeworld to win her favor and gain even more power.

So basically all Cosmic Concepts in Marvel like Chaos, Death, Infinity etc are represented by Avatars so humans can see their form
and the Concept Death, her Champ has been Thanos 
 
 
So no I don't call him 'abstract' but he is her personal and most elite soldier

I think it's just something that people are being disingenuous with. Thanos hasn't been shown doing anything but watching. And there is no proof that he can do anything but be with Death since he himself is finally dead. Personally I'm not even convinced that Thanos would stay where he is now if Deadpool were suddenly able to die.  
 
That's just my opinion, but I think the lady likes Wade a little better. lol.

no

I never thought so

He is currently the Avatar of Death and cannot die, but I still don't think that makes him an abstract entity because his Avatar powers could be removed by Death if she chose. 

I don,t think he is an abstract because he directly interferes in the flow of the universe. Galactus is a quasi abstract because he sometimes interferes. By giving him the new title Avatar of Death things might have changed but I doubt it.

" He is currently the Avatar of Death and cannot die, but I still don't think that makes him an abstract entity because his Avatar powers could be removed by Death if she chose.  "