1) is it easier to reach 800 ELO now or a year ago?
Answer is: it is more difficult because as you have now more players that are ranked higher than 800 than a year ago, a new player reaching 700 will get matched more frequently with higher ranked (more skilled) players than he would have been matched with a year ago. So his probability to win games today is lower than a year ago and his win ratio to move from 700 to 800 will be lower than it would have been a year ago.
This is an interesting perspective, with a conclusion consistent with what I was thinking (having seen opponents' historical ELOs being higher than I would have expected given current skill level). The argument seems circular though, partly because it's unclear how much of the increase in the number of players ranked over 800 is attributable to a higher availability of points / ease of ELO increase (as you pointed out in a previous post), and how much is attributable to a general increase in skill level.
For the argument to be valid; specifically, the premise that one is now matched more frequently with higher ranked (more skilled) players, it would have to hold that the players ranked 800+ now are at least as skilled as players ranked 800+ previously, which is in fact the very thing we're trying to prove/disprove. Further, this decreased probability of winning games given higher-ranked opponents should be a non-factor, since this is supposedly accounted for by the positive opponent ranking vs ELO-at-risk relationship.
I hate to play devil's advocate on a conclusion that I agree with, but alas logic must prevail!
2) is it easier for Hielco to increase his ELO now or a year ago?
Answer is: first point to note is that for Hielco above rationale is not applicable because he is only matched against lower ranked players. Secondly it is easier for him because the pyramid of the ranked players has flattened over time. Now he get matched more frequently against players ranked closer to him than a year ago so his own ELO can increase more easily than a year ago. But the reason why this happened is because he didn't play as many games as many of the other players who came closer to him. If he would have played as many games as the average of the following 200 active players his ELO today would be higher but his ability to increase it would have remained as difficult as a year ago.
Morality: if we assume that another player that has exactly the same skills as Hielco would exist , such player can reach or even beat Hielco only by playing more ranked games than him over the same period of time.
Again I would similarly argue that if we assume the opponent ranking vs ELO-at-risk relationship is truly representative, it should not be any easier now than previously for Hielco to increase his level. In fact, if we assume that his skill has not changed substantially, one could argue that it's in fact more difficult, since his own ELO has increased and he thus gets fewer points than previously when matched against an opponent at some constant ELO.
My stance on Hielco (granted, I've only heard legends and never actually witnessed his skill or its evolution) is that his pursuit of ELO is likely asymptotic; i.e., if he keeps playing, his ELO will continue to increase ad infinitum, never actually reaching his true ELO. The result is that any conclusions underpinned by some assumption of the relationship between his skill and ELO break down, since I would think there be some time-varying delta that persists between his skill and ELO that's difficult to model.
3) is it easier to be in the top 250 now or a year ago?
Answer is: it is obviously more difficult today because today you need to reach a higher ELO than a year ago to be in the top 250.
Morality: the only way to increase your ranking (ELO points or effective rank), assuming you are playing at your true level, is to increase your skills faster than the average of the other players. And to do that you need to just play more games than the average of the other players.
I agree that it is obviously more difficult to be in the top 250 now, but I don't think ELO is a valid basis for the argument since we haven't yet convincingly concluded whether it's more or less difficult to reach a particular ELO level. Rather, it's obviously more difficult now because there are more and more aliases in the Top 250!
If we're talking increasing one's place on the 'clean ranking' though, it's certainly much more complicated than just 'playing more games' than others, since there's clearly a wide variance in players' rates of skill increase. (No offence to a certain "Italian Mountain 4", but 35000+ games and still in silver? Come on.)