Well, who knows what the speedrunners of the future will do! I believe that, as long as there are authorities to keep people from getting away with cheating, which will only get stronger as more and more communities pop up, the integrity of speedruns will be maintained. However, people need to be more vocal when calling out something that's unfair or blatant cheating, and encourage more people to be open to debate. I've been maintaining the HL2 running community for 7 years, and have watched 3 different generations of runners come through, and one constant is that there's a lot of debate always going on determining what's fair and what's not. For the record, that save-deleting thing you mentioned was brought up a lot, and was met with a lot of dissonance before people got greedy and started to force SD into a regular category. I've never been a fan of that myself, but I try to stay out of categories I don't have any knowledge in.
On another note, there will always be a ying-yang to what kind of speedruns people make. I'm working heavily on a new HL2 run, which you'd probably hate :P, but I also plan on making one you might enjoy which stays in-bounds, and is more pure in the eyes of people who turn their noses to more controversial things, like OOB or using scripts too heavily, so who knows! You can't predict the future and all that, but we can shape how upcoming generations will evolve and how they'll appreciate the different categories.
The reason for categories existing is for players who prefer speed runs done with different rules. This whole concept of unsettling trends is pointless. Just watch/play the category you like and everyone will be happy.
This. It's completely unnecessary to try and control what people do in speedruns, in regards to what tricks and glitches they use. As long as someone isn't cheating, and labels their speedrun appropriately, according to category, everyone is as free as you are to make whatever they want to. As far as HL2 goes, new glitches are constantly being discovered, and the runs will continue to be improved upon because of these. This applies to any speedgame out there. Just because you don't like a trend doesn't mean everyone's drop their hobbies, and bends to your desire. Just let them be, do your own thing, and let them do theirs.