I thought the OP was referring to using the singular ‘diocese’ when referring to many/multiple/numerous ‘dioceses’.
I’ll add noticing more and more people not actually pronouncing the possessive ‘s’ when the possessing word ends in an -[consonant]s. So like, “that’s Smithers’/Smithers’s* Malibu Stacy” is said like, “that’s Smithers Malibu Stacy”. It grates!
Right here on the Dope, here’s an example. Just read the very first sentence of this thread right here.
Given the rest of his post and his other posts in that thread, that seems more like a typo than intentional construction.
In my neck of the woods I could find myself speaking with 2 people, one who says: “That thing needs fixed.” and another who says: “I fixded it.”.
I haven’t noticed “assault” for “assaulted” but I have certainly heard/seen “text” rather than “texted.” I think it happens because “text” sounds like it could be a past tense form, along the lines of “vexed” or “flexed.” For someone who hears it that way, “texted” sounds wrong, as though one were doubling the past tense markers.
I have encountered this particular habit more often in the UK than in the US (I can’t speak to other countries). On another forum I belong to, based in the UK and with a huge membership, arguments about the text/texted controversy arise rather frequently. Some people insist that they could never say “texted.” They generally can’t explain why other than to say, “It sounds wrong.”
If it took you a year to locate your first example, I’m going out on a limb to suggest this is not the tidal wave of linguistic doom your OP made it out to be. 
In a more serious vein, I suspect the whole thing is BigT’s contention of folks eliding sounds, rather than an effort to ignore declensions.
Coupled of course with txt-writing, where *every * orthographic / linguistic convention is sacrificed in the single-minded pursuit of using fewer characters before hitting [Send].
Not something that forms a regular topic of conversation with me, but that’s always been the standard pronunciation for the plural that I grew up with. Or did you mean that’s how people are pronouncing the singular?
I wouldn’t be surprised if we start hearing “diosee” as the singular, the same way a lot of people say “specie” as the singular for “species.”
Me too. One DYE-oh-Cease. Two DYE-oh-Seize.
One I’ve noticed on occasion, and from folks who ought to know better, is “incent” used instead of “incentivize”.
When I was a kid in the '70s, I only heard “versus,” pronounced in full.
My guess as to what happened is that some people started to parse the phrase differently.
So “Ali versus Foreman” is “Ali against Foreman” - noun-preposition-noun.
But some people stated parsing it as subject-object-verb - “Ali opposes Foreman.”
So if it’s a verb then “verse” makes sense as part of a conjugation.
I think there’s a second thing going on in which people think it sounds wrong to repeat sounds. So Charle’s instead of Charles’s, tex’d instead of texted, etc.