There is Marketing strategy behind this, of course, but the other reason is Political, as its an attempt to further bond desired ties between the "Region-State" & the Club. Said in another way, FC Barcelona wishes to remain & continue being synonymous with Cataluña.
Perfectly acceptable & the Club is perfectly free do choose as they wish in a democratic society, but surprisingly "village" & "small minded" ( my opinion ) for a Football Club with their dimension, their proclaimed universality ( they sponsor UNICEF ) & global reach, they have more fans outside the Catalonian region & outside Spain. In my humble opinion it is bad business mixing Politics with Sports, it has always been the case however much used & abused throughout history for propaganda purposes. This unfortunately has that smell.
Some may ask what about the other Barcelona city Club RCD ESPANYOL? Are they less Catalonian? Are the Espanyol fans less? Will this cause other Spanish Football Clubs to change their uniforms for their Region?
I take it that Barcelona has announced their intention a year early to sample the public opinion. It will give conversation for sure. Meanwhile fans prepare for another 90€-100€ to get the new uniform.
Perhaps FC Barcelona should consider giving a shirt for free for the entire Regional population, right? Doubt it, the nationalist sentiment does not go out that deep, business will always be first, "Politics" will be the instrument to keep the faithful in line with their credit cards handy & the business churning out the euros.