Neurons are only part of the brain (50% ?). Glia have been shown to be part of the NMDA repair/replace cycle [0]. And that's just some prelim stuff. We've no idea what else the other cells may/not be doing yet. Just replacing neurons is unlikely to replicate a brain's functions. You need the whole caboodle.

[0] https://duckduckgo.com/?q=glia+cells+NMDA&atb=v173-1&ia=web