Eh, this is a trend which has been in process for a number of decades. It seems that English has been getting more 'fluid' in terms of the boundaries between types of words. Back when I was in grade school nobody would have even known what you were talking about if you said you wanted to "conference with them", there was a verb form of that 'confer', "I would like to confer with you." However, by the 80's school teachers were happily 'conferencing' with people left and right (and making many of us wince).
Things like using 'murder' as an adjective are no more foreign to me than that. I don't think that kind of usage ONLY started in the 21st Century. As with the above noted use of nouns/adjectives as verbs, it was already a trend in the 80's, probably earlier in some places. Maybe it is more common now, and maybe that weighs in your evaluation of the most likely first date for 'murder hobo', you'll have to use your own judgment there. It is hard to know how accurate a retro-projection of what seems odd or not really is, but I'm not feeling like 'murder hobo' has an exceptionally 'only in the last few years' ring to it. English has been getting 'bent' this way for a long time...