I’ve tried Marmite but it was so salty it was virtually unpalatable even in small quantities except as a salty seasoning additive to other foods. Why all the salt?
What is the flavor base note of these spreads without all the salt?
Yeast.
(Seriously, asking what Vegemite tasts like without the salt is rather like asking what candy tastes like without all the sugar.)
It would have a fairly bland umami flavor. If you taste plain yeast, you can tell that it’s more-or-less the same flavor as Marmite, but less concentrated and with less salt. You can also dissolve a spoonful of Marmite in a cup of hot water for a tasty broth of similar flavor.