PVP build flexibility

My post in QA might have been in the wrong place and had the wrong title so here it goes:

I am levelling up a El/Ms a Mo/Ra and a Nc/Wa as RP chars.

By doing this I hope to unlock absolutely all the skills. This means my last slot will be a very flexible pvp slot.

Will I be able to unlock everything usable by all primaries this way (runes/items?) am I missing some flaw?

PVP characters have access to all the same GvG/PvP areas an RP char does as far as I know. Just no questing.
You can unlock runes for a class even if you don't play that class. For example, all of the runes I have managed to come across so far have been for a Mesmer. I play as a Warrior/Necromance...Totally useless to me in PvE. And from what I hear you can change your secondary class once you hit level 20. So in a sense, you could have one character, any build, and after some extensive play could have unlocked all skills, runes, and items.

but the only thing you have to remember is that you can only change your secondary profession,
so if your primary is a warrior it's always going to be a warrior.
So that extra pvp slot will be in handy if you decide to change things around for a little more flexibility. Aye that would be the idea. I would just remake with the same name and can be whatever took my whim...

It would leave everything open...