As I mentioned in a comment, the gemara in Shabbos 115b cites a Tosefta condemning those who write prayer-books (and amulets) with G-d's name: "...מכאן אמרו כותבי ברכות כשורפי תורה". While I could hear of a possible leniency with regard to writing the texts of brachot without the names of G-d explicitly written (e.g. by employing encripted spelling such as "יי" in place of the Tetragrammaton and using a single character that combines the א and ל for other divine names based on that root), explicitly writing the names doesn't seem to have any heter that I know of yet. In addition, most of the siddur is based on verses of Tanach which I believe have the same issues of shaimos as divine names even when they do not include one.
(Even if one were to argue that [akin to the leniency we have nowadays for writing/printing divrei torah in spite of the original prohibition of that practice] there is a reason nowadays to have printed/written texts of the prayer services, I find it very hard to believe that there would be an "eys la'asos..." nowadays for printing or writing the actual divine names in that context that would not have already been extant at the time of the writing of the Tosefta and Talmud.
(In addition, I believe there are laws of sirtut (etched lines) etc. for ksav ashur for which reason I believe (?) Rabbi Herschel Schachter of YU prints/writes his responsa and exams in Rashi script.)
