I have purchased an apt in Jerusalem, and am planning on being there each year, iy"H, for the rest of my life for pesach and sukkot at least. Shavuot is uncertain at this time. Must I still observe yom tov shaynee shel goliot?

Mazal tov on the purchase of your apartment in Yerushalayim. May this apartment be your full time residence. In the interim time until you do so, coming to Israel for the period of the Yomim Tovim alone does not yet constitute that your residence in Eretz Yisrael which would allow you to keep one day. Rav Shlomo Zalaman Oirbach zt"l(Minchat Shlomo 19:7) did say however, that if a person comes with his family for all three of the yomim tovim, Pesach, Shavuot and Sukkot then he may keep only one day. This is because his presence here for all the "regalim" makes him in regard to this particular mitzvah as if he lived in Israel. This would not apply though, if one were here for only two of the "regalim." If you are here for only two of the three, I refer you back to the answer of Rabbi Blass upon which you based this question, who already addressed this issue and referred to the various opinions among them that of the Chacham Tzvi which was also upheld by Rav Goren zt"l. (Torat Hamoadim pg.258). Gmar chatima Tova