Yes. After much consideration, we have changed our official recommendation and are now advising that female cats be given a 50-100% vegan diet and males a 25-75% vegan diet.
Because vegetable protein is less acidic than meat, a strictly vegan diet can cause a urinary pH imbalance that can lead to crystal formation, "infection" (really inflammation, but usually called by the wrong name, even by vets), and, in males, blockage of the urinary tract.
Although we have always given advice on how the risks of this happening may be mitigated while giving your cats a strictly vegan diet, we have found over the years that many people have not followed our advice very closely, their cats have developed urinary tract problems, and they have ended up switching away from vegan cat food entirely. There are also some cats who are so prone to urinary tract problems that even when all precautions are taken, their pH may still periodically become too high while on a strictly vegan diet.
Our mission as vegans in general, and as a vegan company in specific, is to limit the amount of animal suffering in the world as much as we possibly can. Although it may sound paradoxical, we have come to believe that advising people to feed their cats only a partially vegan diet will have the effect of decreasing the total amount of meat cat food being purchased by the vegan community and therefore the amount of suffering for which we are collectively responsible.
Consider, for example, a case in which a vegan feeds their cat a strictly vegan diet for one year, whereupon they experience a urinary tract incident and switch back to meat for the rest of the cat's life; for simplicity, we'll say nine years. Over the course of that 10 year period, 10% of the food eaten by that cat has been vegan, and 90% meat.
Now consider the difference if this same person had taken a more conservative approach and only attempted to make their cat half vegan in the first place, and the urinary tract problem were avoided entirely. Over the same ten year period, only 50% of the food eaten by this cat would have been meat, a decrease of 40%. Multiply a 40% decrease in meat consumed by the total number of vegans and their total number of cats, and it is easy to see how quickly this benefit would accumulate.
The ranges given (25-75% for males, 50-100% for females) are approximations based upon whether or not a given cat has had urinary tract problems in the past, what food you are giving them, and how vigilent you honestly intend to be about getting their pH checked regularly, etc.
Females-- who, due to anatomical differences, cannot become blocked and to whom urinary tract problems are therefore much less of a serious problem-- can be completely vegan unless they have a history of chronic urinary tract issues. It is strongly recommended, however, that you not feed them an entirely dry food diet if you intend to make them completely vegan (see more recommedations below).
Males who have not had urinary tract problems in the past and who eat mainly wet food (especially Vegecat pH) can probably get by at the top end of the range (50-75% vegan), while males with chronic problems and those who mainly eat kibble should remain at the low end (25-50%).
You may either alternate meat meals with vegan meals, or make every meal a combined part-meat/part-vegan meal as you prefer.