Alot of times when I start a text to my mom I start typing mom under contacts in Textra. My phone I can search that way in contacts as I have my mom listed with her name and (mom) is her nickname.
So back to Textra I start a text with (Mom) and her contact only comes up if the mom is listed in the text body. So if be cool if Nicknames would show up in Textra search from my phone contacts