TSPHP envisions that code written in TSPHP will result in better code quality overall.
It shall be an addition to PHP and not a replacement and serves as the type-safe alternative of PHP for all those users who actually want type safety in PHP. It especially does not intend to change the PHP core and thus everyone which does not want type safety can stick with PHP.
In a very long term, TSPHP envisions that frameworks will be written in TSPHP and normal PHP users (as well as TSPHP users of course) can use the output/outcome.
More as a side notice, TSPHP does not intend to compete against Facebook's HHVM project (including Hack) and believes that there are several opportunities for joint ventures between the two projects.