Legendary weapons should be what they were always intended to be. A fancy skin, and that’s it.
The stat swapping on legendary weapons should carry over to all ascended gear. Your sigil swapping idea should carry over to all ascended weapons, and all ascended armor should be capable of rune swapping. All ascended gear should also be capable of infusion swapping.
As it is, getting a full set of ascended gear isn’t that much of a grind; it’s within the realm of reasonable grind IMO. Getting a full set of close to optimized ascended gear for dungeons and fractals in a team setting is a colossal grind. Getting a second set of ascended armor with Strength runes for solo and uncoordinated group play is an additional grind, but it’s not as bad as getting a ton of ascended weapons (even if you more or less skimp and just get say force/frailty, force/justice, force/night, and force/undead combos, along with a bit more weapons you normally won’t use for situational purposes).
Then we’ve got WvW, which is going to demand at least one different set of gear, because you’re probably not going to want the same stat combinations you would in PvE, nor are you going to want the same sigil/rune combinations. And we’ve got WvW infusions, too, which can make a noticable difference when taking things like fully upgraded camps with a lowish number of people. And we must consider that hey, perhaps someone might want to run different builds in WvW, and in many cases, this again demands another set of gear…
Let’s not forget people with multiple characters, who want to do lots of different things with those characters, either.
For example, I might really want to play a condition warrior in WvW in addition to what I normally play there. It could be very fun for skirmish-style play. But I’m not going to invest in a set of rabid gear with runes of the krait, and some weapons with doom/earth sigils to do it. Especially not ascended gear, which due to WvW infusions (what does one typically do in small group WvW play? Take camps. NPC damage reduction and damage increase helps.), and a few percent damage reduction over exotic gear, and ~6% damage increase, would really shine here. I’m sure it’d be fun and interesting to play. But is it worth even the time cost of doing it in Exotic gear, much less Ascended gear? Not even close.
One of the appeals of Guild Wars for me, was the ability to run an optimal (as best as I could determine it) setup on any character I wanted with relative ease, allowing for a great deal of fun experimentation playing different builds with the same class, even different classes, and knowing that it was my player actions that dictated success.
Lots of grind to play different builds and classes? Not fun. Extreme tediousness of managing all the items? Not fun. I thought that ANET said grind wasn’t fun, and they didn’t make grindy games. Well, the grind for ascended isn’t too bad, until you factor in how compounded that grind gets for multiple builds and multiple characters, and it’s really unfortunate. As far as I’m concerned, this is mostly a design oversight on their part. An oversight they really should fix.