This Sunday, it was teased that the next TTFC Spin-Off will come out on June 27th. Though no details were revealed on whom it will focus on other than letting us know that it's a "Kamen Rider × Kamen Rider" Spin-Off.
Today, Toei had launched Toei Online Store and it looks like they didn't restrict some of the information on the page. Among the Titles starting with 「か」(ka), it had also listed "Kamen Rider Specter × Blades". This could possibly be the title of the teased spin-off.
The previous Kamen Rider Saber × Ghost ended with a cliffhanger where Kanon Fukami was taken away by Kamiiyu & Muller. There were also some mysteries left to be answered in this spin-off. So Kamen Rider Specter × Blades might be the sequel to Kamen Rider Saber × Ghost.
Kamen Rider Specter × Blades title has been now removed from the 'Ka' category. Along with this, the Kaizoku Sentai Gokaiger is also missing from the same category. It is expected that Gokaiger has something coming for the 10th Anniversary. But this confirms it.
Basically, all the TTFC Titles have been hidden from the website. So the upcoming Kaizoku Sentai Gokaiger announcement could possibly be related to TTFC too.