they way i understand it, because immune system is basically constantly fuzzing all potentially new things, what is important is how antigen looks like on the surface. what it is made from matters less, and whether aminoacids there are l- (natural) or d- (not) it shouldn't matter that much, antibodies are generated for nonnatural achiral things all the time including things like PEG and chloronitrobenzene. then complement system puts holes in bacterial membrane and that's it, it's not survivable for bacterium and does not depend on anything chiral. normally all components are promptly shredded, it's a good question if that would happen too but, like - this might not matter too hard - there's a way for immune system to smite this thing

the potential problem is that peptides made from d-aminoacids are harder to cut via hydrolases and it's a part of some more involved immune response idk details. there's plenty of stuff that's achiral like glycerol, glycine, beta-alanine, TCA components, fatty acids that mirrored bacteria can feed on without problems. some normal bacteria also use d-aminoacids so normal l-aminoacids should be usable for d-protein bacteria. there's also transaminase that takes d-aminoacids and along with other enzymes it can turn these into l-aminoacids. but even more importantly we're perhaps 30 years away from making this anywhere close to feasible, it's all highly speculative. there's a report if you want to read it https://stacks.stanford.edu/file/druid:cv716pj4036/Technical%20Report%20on%20Mirror%20Bacteria%20Feasibility%20and%20Risks.pdf

also look up cost of these things. unnatural aminoacids, especially these with wrong conformation but otherwise normal are expensive. l-tert-leucine is unnatural but can be made in biotechnological process, so it's cheaper. for example on sigma-aldrich, d-glutamine costs 100x more than l-glutamine, and for sugars it's even worse because these have more chiral centers

besides, it's not really worth it probably? it will take decades and cost more than ftx wiped out. other than making it work just to make it work, all the worthwhile components can be made synthetically, maybe there's some utility in d-proteins, more likely d-peptides, tiny amounts of these can be made by SPPS (for screening) and larger in normal chemical synthesis (for use). these might be slightly useful if slowed down degradation of peptides could be exploited in some kind of pharmaceutical, but do you know how we can make it work in other way? don't put amide bonds there in the first place and just make a small molecule pharmaceutical like we can do (as in, organic chemists)

another part of the concern is that these things could transform organic carbon in form unusable to other organisms. but nature finds a way, and outside of fires etc, there are bacteria that feed on nylon and PET, so i think this situation won't last long