I don't think its a patent issue - its a copyright issue with the code/software.  The fact that the patents are expiring might mean that more converter options are available as people don't have to work around patents anymore, but whatever software they write will still be copyrighted and those distribution rights reserved (as they are with the Lame converter today.)

Lame is freely distributable for non commercial use.

Once a company eg Cakewalk includes it in a product it is no longer covered under the free use licence making licence fees payable to the licence/patent holder (Thompson) on a per unit basis.

Yes Cakewalk could absorb the cost but at $10 per unit sold would be a hefty amount. So install it yourself for free or pay Cakewalk. If you check Cakewalk is a signatory to the agreements with Thomson.

The thing you don't usually hear in these discussions is why you should choose your mp3 encoder carefully.  So many of us jump through all kinds of hoops to use just the right microphone or plugins for our productions, yet at the tail end of the process, grab whatever mp3 encoder is free or convenient. 
 
But not all MP3 encoders are alike.  Here's an article that explains the hows and whys:
 
http://archive.arstechnica.com/wankerdesk/1q00/mp3/mp3-1.html
 
Personally, I've used dBpoweramp for years.  It isn't free ($39) but is arguably the best when it comes to being full featured in all things mp3 related (including ripping CDs).

It happened a little sooner than I expected. From the 2017.04 release announcement

Alex Westner [Cakewalk]

MP3 Availability

Artist, Professional, Platinum
MP3 export is now available in SONAR Artist, Professional, and Platinum at no charge. Recently the patent royalties associated with MP3 encoding expired. Cakewalk is excited to offer MP3 encoding free of charge in SONAR.

Freeeeeeeeeeeeeeeeeeeee at last!!!

JonD
The thing you don't usually hear in these discussions is why you should choose your mp3 encoder carefully.  So many of us jump through all kinds of hoops to use just the right microphone or plugins for our productions, yet at the tail end of the process, grab whatever mp3 encoder is free or convenient. 
 
But not all MP3 encoders are alike.  Here's an article that explains the hows and whys:
 
http://archive.arstechnica.com/wankerdesk/1q00/mp3/mp3-1.html
 
Personally, I've used dBpoweramp for years.  It isn't free ($39) but is arguably the best when it comes to being full featured in all things mp3 related (including ripping CDs).

I looked at dbpoweramp for years but I can't bring myself to buy it because the owner is a complete arse.

abacab
Freeeeeeeeeeeeeeeeeeeee at last!!!

Couldn't have put it better myself

Does anyone know if its the same encoder they have been selling?

dwardzala
Does anyone know if its the same encoder they have been selling?

I believe that there is only one "real" MP3 encoder that was used by licensing the patent.
https://en.wikipedia.org/wiki/MP3
 
The alternative has been to use the LAME encoder...
http://lame.sourceforge.net/

dwardzala
Does anyone know if its the same encoder they have been selling?

I see no change from 2017.03 to 2017.04 WRT the integrated mp3 encoder. The mp3 dialog still shows SONAR is using LAME to create mp3 files.