The answer to this is a plain and simple No. You can hang on to the one reason people went with IAX/IAX2 back in the day, NAT. Honestly this is not longer the issue that it was 15 years ago. Outside of the fact that routers have improved their NAT capabilities (most at least), the rise of IPv6 being used and the fact that numerous Telecom/LECs/ISPs are now doing dedicated peering/connections to end users. IAX was created during a time when SIP, H.323 and MGCP were still fighting to be the “prime standard”. That time has passed, we known who won that. Since then everyone has adjusted accordingly.
Now take all that off the table and just look at IAX2 over the 4-5 years. Reviewing the change log you’ll see Digium’s activity on IAX2 come to an almost sudden stop around the end of 2015 because it went to Extended support by then. That means Asterisk developers are no longer handling those issues and the community/contributor’s are where those issues are handled now.
2016 saw only one change for IAX and that was to remove plaintext auth support as it’s deprecated and was slated to be removed in Asterisk 16 (which I think it was).
2017 saw four issues dealt with and 50% of those was dealing with Netsock being deprecated and removed from the Asterisk core but since IAX2 is the only thing still requiring it the changes where to move Netsock into IAX2 only.
2018 saw a single issue handled.
2019 saw zero issues handled for IAX2. In fact the only mention of IAX2 in the 2019 changelogs is from Matt Jordan in regards to a new metric that was added for PJSIP and might work with Chan_SIP and IAX2 but never tested (because they are deprecated).
(And why are you still using IAX2 and [CHAN_]SIP? It’s 2019 folks. Get with the program.)
At this point the vendor who created the protocol is wondering why people are still using it and the changelog is showing that less and less are contributing to the maintenance of the protocol. So Matt’s question is valid, why would you use IAX2 in 2019? It’s just not wise.
Just remember that Asterisk, FreeSWTICH and 3CX (I believe) are the major players that support IAX2. While they have a decent share of the business PBX market they don’t own the space and well VoIP providers that support IAX2 are considered niche providers for a niche market.