This doesn't change anything for Mevans when updating the mod. With 1.7.10 -> 1.14 many, many internal names already changed, and changed names are the least problem with updating. If some things have another name in 1.15 again, this won't affect Mevans that much. Also, they didn't deobfuscate the code, but release some of the obfuscation mappings they use - but not all (mappings for params etc. are missing). The change is especially interesting for things like Forge, because this eventually simplifies their infrastructure. Though the code is still obfuscated at runtime, so mods still have to deal with obfuscation. The only change is that the names for some things are no longer delivered by the MCP or the community, but by Mojang (but Forge will probably keep some names anyway, because the way Mojang names some things is not always ideal for modders...).