Guild Wars 2

If we wont be able to unlock abilities using skill points then how will we unlock them?

The summary of the stream in which this was explained says the following:

Most skill and trait unlocks will cost five Hero Points. While the numbers should not be considered final or absolute, Jon estimated that it will require roughly 465 Hero Points to unlock every trait and skill available to a character. The process of leveling to 80 will award about 400 Hero Points, so players will only need to complete a fraction of the available hero challenges to have enough points to unlock everything. The system is designed to give players access to skills and traits much faster than in the current system, with the number of Hero Points gained from leveling set to increase at higher levels.

Using Hero Points obtained from leveling and doing skill challenges.

But would it be best to use my skill points now that all chars has every ability or rather wait and let them be transformed into crafting mats when expantion hits?

I’d hold onto them.