This would be an optional exstension. I think that by implementing chunk loading and NBT loading into a native extension, server owners could speed up their servers. @dktapps has already created an extension for chunk utils: https://git.io/v9mav @shoghicp (yes, i know its not really him) created an extension a while ago (2014!) which contained native code for level generating, math operations and the binary class: https://git.io/v9mal By implementing both of these plus NBT into an extension we could (hopefully) speed up important aspects of PocketMine for server owners who would like to. Why NBT in this extension? The current NBT implemention is bad (#blameshoghi). Obviously the current library needs a rewrite but we could go one step further by implementing it in this extension. But we are busy! We have more important things to worry about! That's not a problem. This isint a top priority thing, i just thought i'd make the suggestion. Why did you use git.io in this thread? Because i can. Please feel free to vote on the poll.
This isn't a new idea. As I said on GitHub, C-ifying it isn't going to magically make it faster. There are significant barriers to implementing a full-featured NBT library into C, and a matching PHP implementation to make it optional would be far more difficult. If any such extension is created, it will be mandatory.
A poor design of the NBT framework has nothing to do with making it into C. It can be well-rewritten in PHP without any design issues.