That's exactly what I thought too. Imperfect crystals have already made an appearance in The Force Unleashed (which served as an episode 3.5) with exactly that effect. Every force user had a slightly unique hilt on their saber anyway. With less guidance (and tradition) available, more variation makes sense.
Time to nerd out A decent theory I saw on another forum was that with the resurgence of force users, there is a shortage of the already rare lightsaber crystals (that need great care to produce) and so the (supposed) sith in the trailer is using a saber with an imperfect synthetic crystal, making the blade look frayed, but…