I noticed that Google Maps has been updated to show a northward extension of SH 289.
It used to terminate at SH 56 (OLD US 82), but now has been extended north to a terminus at a county road near Lake Texoma; with no possibility of being connected to anything. It makes sense to extend SH 289 up to US 82; to me that should have been done when US 82 was realigned. However, the only value of continuing the SH 289 designation up into the lake area is 1) Route number continuity and 2) Funding. It seems a little odd that a State Highway ends at a county road with no chance for extension.
http://maps.google.com/maps?hl=en&ll=33.655209,-96.512833&spn=0.380655,0.802002&t=m&z=11
There is a bit of a mapo involved; I checked into what Google Street View shows and the state maintenance stops at the Elks Road turnoff (
http://g.co/maps/2fbh7) across from Island View Park. The picture still shows FM 120 signage since Google hasn't taken a Street View trip up there since before the TX 289 extension (and FM 120 replacement north of Pottsboro) was completed. The rest of the road up to the end at Preston looks to be county or locally maintained.
From what I can tell, the TX 289 extension directly benefited North Texas Regional Airport, Pottsboro, and the Tanglewood resort (whether they had a hand in trying to get TX 289 extended or not).
There are many FM/RM roads and a few primary TX state highways that don't end at another numbered road. Unusual, sure, but not rare.