Hello David,
Yes, an interesting Sewar/whatever!
The laminated blade looks old and I'd have no qualms to believe it to be sometime from the 19th c.
As usual, the crosspiece/mouthpiece of the scabbard is from horn and well-carved in fine detail. Either this got removed from SE Asia rather early or it might be somewhat later IMHO. The scabbard stem will be wood; if any of the silver covers could be slided off, some more info might be gained.
The silverwork on the scabbard may be medium craftsmanship, the quality of the hilt less so IMHO. Since the latter's motifs are not en suite, I'd guess that it got restored/replaced later, possibly after WW2.
I don't see any stylistic hints for this piece to come from any of the highland groups. This most likely is a Malay piece and originates from the Sumatran East coast or the western Malay peninsula.
Historically, there probably never was any clear-cut preference for staining these blades with warangan. There are colonial accounts that staining with warangan was known and practised in Aceh (sometimes, not universally). This is also seen in some examples that appear to remain in old, original stain; OTOH, many blades in museum collections exhibit low-contrast stain compatible with fruit acids or vinegar (or no remaining visible stain at all).
Most laminated blades from this region are forged from low-contrast steel (which still can look very nice if stained) while some are obviously intended to exhibit pattern-welding with stronger contrast. Thus, it wouldn't hurt to give it a try IMVHO.
Regards,
Kai