I think that if you're going to implement a new chat, it should at least have all the features the last one did, which yes it's a lot of work, but you're the ones trying to make something new instead of working on what already exists.
- the chat completely clearing when the map changes is bad;
- the inability to select and copy text from the chat is bad;
- the menu flashing for a split second when you press esc while in the chat is annoying;
- the name autocomplete half of the time taking you to the start of the message is detrimental;
- minorly, since I don't think most people even use it, the new chat doesn't have filters like the last one;
- pressing u doesn't open the chat on team_say mode, doesn't even open the chat at all;
- a rare bug that literally never happened before this chat, I don't know if it has happened with anyone else, but has happened to me 3 times: I frequently alt tab, possibly while using the chat in between, my game got stuck in a state where I couldn't go back to the main menu, no matter what I did, pressing the console button doesn't work, pressing esc doesn't work, alt tabbing trying it again many times doesn't work.. this rendered me unable to leave the server or join another server unless I had a bind for leaving or I force quit my game on shift tab.
- typing ahg_chatannouncement_interval 0 in console with this current chat causes your game to get incredibly laggy and later periodically freeze, making it incredibly difficult to set it to another value, not very likely people would type that, but this was a troll message people typed before, that that is the command to stop the announcements. On the original chat it just spammed the absolute shit of your chat, in this chat it lags your game too.
- the above situation ^ implies there are performance issues with the new chat, possibly because there is no limit to the amount of messages it can hold, it's only being mitigated by it being cleared every map change or every time you rejoin, but as I mentioned, that isn't a plus.
While I can understand the want to do a bunch of cool things, this is a lot of work you're setting yourself to do.
You could try giving yourself more time to polish it before putting it on the server, or you could do way more work every day than you're getting paid for, if you're even getting paid for it. A server isn't built in a day nor a month, nor was GMod.