TxDOT has posted materials for the Spur 399 public meeting.
http://www.keepitmovingdallas.com/Spur399PublicMeetingThis is part of the EIS process in which the two previously identified alternatives are being studied in more detail. There's no news in this meeting. However, the information provided makes me think there is a very high probability that the orange alignment, east of the airport, will be selected, especially because the City of McKinney is "strongly opposed to a freeway west of the airport". However, another influence not mentioned in the materials is the alignment of US 380 freeway north of the existing US 380. It probably would be desirable for Spur 399 to connect to the US 380 freeway at the point where the US 380 freeway will veer north. (See map shown 25 seconds into the presentation video.)
Both options are expensive, possibly due to 2+ miles of bridges on each option.
Purple option, west of airport: 4.4 miles long, 117 acres ROW required, $601 million. It will displace a large Amazon distribution facility.
Orange option, east of the airport: 6.25 miles long, 233 acres ROW required, $706 million.
The alignment recommendation is expected in summer 2022.