I think it will be years before anyone reaches level 15 or so, so this proposal is mostly moot for a long time.
As for these specific items, I think the first one is unbalanced to the point of being broken at Epic level.
Boots of the fencing master (AV1):
lvl 7 and give a +1 to AC an Reflex when the wearer shifts...
lvl 17 they give +2?
lvl 27 they give +3?
As it turns out, I have a 17th level Druid with Boots of the Fencing Master in my home game and she shifts nearly every single round via Agile Form and Wild Shape. Giving her a +3 AC and Reflex due to a single item is extremely potent. She already has a lot of other defense boosting feats and items (such as Back to the Wall, etc.).
Ring of the Dragonborn Emperor (AV1):
lvl 15 gives +3 dmg to close attacks...
lvl 20 gives +6 dmg?
lvl 25 gives +9 dmg?
I also currently have a 17th level Fighter with a Ring of the Dragonborn Emperor in my home game and she has three close burst Encounter attack powers and she is modeled to have a high chance to hit (bastard sword, one handed weapon talent, Kensei). Once per day, she can get one of the close burst powers back via the ring. By the time she is epic, the 20th level version would probably add about 20 points per encounter more damage (except in solo encounters). This item is not as egregious, but with the sheer number of synergies at epic levels (like ways to get all foes next to the Fighter beyond just Come and Get It), it starts becoming problematic.
But, here is the issue. One can typically have a few +1 bonuses to hit or to defenses. But, even stackable +2 bonuses get out of hand quickly. +3 is broken from the word go.
Let's take an example. Say a PC had all of the normal items and has an AC of 40 at higher level. He gains three different ways (feats, items, etc.) to boost his AC by 1 and he synergizes his PC such that he gets all 3 of these conditional boosts work most of the time. That's AC 43 a high percentage of the time. He's 3 better than normal the vast majority of the time which is pretty darn good.
Now, the DM adds in certain house rules so that conditional items and/or feats can go to +2 or even +3.
Now, he suddenly has an AC of 49. 9 better.
Power creep is real easy to add. With respect to "to hit" and "defenses", no one source should get above +1 or it can quickly get out of hand.
One other comment on this. Even at mid-Paragon levels, PCs are fairly awesome. They have so many different options that it is extremely difficult to challenge them. Boosting their defenses or damage beyond what WotC allows makes it even that much more difficult to challenge them.
This is why I like to limit the game to what WotC hands out. WotC is self correcting. If something gets out of balance and they find out about it, it quickly gets updated.
Just making "bigger, badder, better" item proposals throws that self correcting balance out of whack here at LEB. IMO.
I don't think that the judges should be voting in stronger items without understanding the impact that those items can have at paragon and epic levels.
