True the way I play the best I could do is change some Blade perks for Axe perks, or Heavy Armor perks for Light Armor perks. But for me that's still a completely different character than the one I was just playing.
I don't really see why with your One-Handed example. The skill applies to daggers, axes, maces, and swords equally so your damage gains for each of these weapons are quite equal. By then, I look at it as being your character in expert in one-handed weapons in general, which means a change from blades to axes is hardly a large impact.
Now, I will admit your Heavy to Light Armor situation is quite different. However, if you actually took the time to master both Light Armor and Heavy Armor, I hardly see the need to complain. Perks don't define your character in-game the way that your skill levels do. Perks only augment your mastery of a skill. If you had mastery of both skills, I see no reason why it wouldn't be feasible to migrate perks over, you've already put in the time to master both. That is just the way I look at it anyway.
@Frank.White
While I would hope for new perks, I'm not certain I see how useful that kind of feature would be as they could only add one or two extra without completely breaking the build situation. Most characters max at Level 50, which already leaves builds rather unique and limited. If they tacked on one or two new perks, they'd be ok, but if they added more than that they would likely make builds even more limited than they already are.