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Issues with original idea: Not too many. You will see the goldilocks 50% chance to hit zone move by about 6 levels (proficiency changes and magic weapons/armor). It keeps the range something you can more easily manage. It makes simple +x magic items more palatable to put in-game, but makes combining them with spells far less interesting. It could shift your player's prepared spells and use into a more damage oriented configuration.
The DM using this modification would also want to think very carefully about how many +x items are given. At a point, sooner than vanilla 5e, the players will start trying to vend +2 and +3 shields or armor if they already have a similar bonus equipped.
I think the proposed change is solid for game balance and allows the freedom to use +x items without worrying too much, however, the changes also introduce a potential economy balance problem which could exacerbate vanilla 5e's already near useless piles of gold (yes debatable). That is to say, it still behooves the DM to throw out lots of unique and varied magical items, though the proposed changes allow higher end +x items to be apart of that variation.
The solution to the same problem I found and currently use is to find ways to depreciate ability scores. I altered my system to make every character MAD, and applied it to the world. The foundation being making dexterity the attack modifier for all physical weapons and strength the damage modifier, then applying a similar principle to each caster type, finally making sub 11 Con scores non-suicidal. Brings everything into a more perfect alignment, from Giants to Kobolds. Admittedly I chose to put maximum effort into the endeavor and ended up writing out a massive document changing a solid % of 5e, but the results have been very entertaining. Tons of stuff has been fixed, very little has been broken, and the active game overhead has only increased a small amount.
