One of the cool things about open source is that other people can do that for you! I've released a few bits of (rarely-used) software to open-source and been pleasantly surprised when people contribute. It helps to have a visible todo list so that new contributors know what to aim for.
By the way, there will always be things to add! That feeling should not stop you from putting the source out there - you will still own it (you can license the code any way you like!) and you can choose what contributions make it in to your source.
From the encode.su thread and now the HA thread, you've clearly gotten people excited, and I think that by itself means that people will be eager to try these out. Lossless codecs have a fairly low barrier for entry: you can use them without worrying about data loss by verifying that the decoder returns the original data, then just toss the originals and keep the matching decoder. So, it should be easy to get people started using the technology.
Open-sourcing your projects could lead to some really interesting applications: for example, delivering lossless images on the internet is a very common need, and a WASM build of your decoder could serve as a very convenient way to serve HALIC images to web browsers directly. Some sites are already using formats like BPG in this way.