Not quite so. Problem seems to bee not in ease of decarboxylation, but rather in O/N alkylation selectivity,
which in more sterically congested haloacids shifts toward O and gives wrong products. Nevertheless, I have reference to: V. Auger, Bull. Soc. chim. France [3], 23, 333 (1900) ,which claims, that using alpha-bromopropionic acid in Kolbe method gives nitroethan with yield 50% (thats even better than nitromethane yield from chloroacetic acid) No, I don't have original paper and don't know, if the methodics differs from nitromethane one. Alpha-bromopropionic acid one can probably make from lactic acid and hydrobromic acid boiling them together and distilling or something, but don't quote me on that.