CHRISTIANS, TEFILLIN, & SUKKOTH
Someone once mentioned similar logic as to why we don't do something due to Christians. I asked him whether it would become forbidden to wear tefillin if Christians started wearing tefillin. He said yes! I was afraid to inform him that there are already Christians who wear tefillin! Perhaps he would say that we need to wait until all Christians start wearing tefillin... but then he'd need to define what a Christian is. Not all Christians consider other Christians to be "true Christians." Perhaps we should wait till all the world wears tefillin... and then we'd stop wearing Tefillin?
...perhaps during the Messianic era when the entire world will make teshuva (repentance) and return to G-d, we should then cease walking in His Ways? hhas w-shalom.
The prophets taught that during the days of Moshiahh G-d will even coerce the non-Jewish nations to celebrate Sukkoth in Jerusalem! We don't know to what extent they'll celebrate Sukkoth, but the prophet is very clear - Zekharya 14. And do we see that at that time the people of Israel will be required to abandon celebration of Sukkoth? Heaven forbid! It is the HaShem's Will that the nations be influenced by the people of Israel to walk in His ways. Unfortunately, some Jews have become so insular that they don't even know the ultimate goals of Torah - to elevate the entire world, through paths of peace.