Passover celebrates Christ, He is the Passover lamb. Pentecost celebrates the giving of the law both under the old and new covenants. These are not in the future. The Fall feasts are celebrating the future.
And it is the plan of salvation we celebrate, not prophecy.
The Only reason I can see for a Christian to partake in any of the Jewish feasts is if they are invited to do so by Jewish friends or family. Or if they converted from Judaism and they do it out of tradition.
Otherwise, it is too desirable for the slaves to slip back into slavery. Like a cigarette smoker, who has quit, telling you it is ok for them to smoke only 1 cigarette on the "holidays".... Maybe it wouldn't hurt a regular person. But the one inclined to cigarettes already it is just a major temptation. Probably one they don't want to even acknowledge because they are attempting to excuse it by just doing it on the "holidays".
Galatians 5:1 Stand fast therefore in the liberty wherewith Christ hath made us free, and be not entangled again with the yoke of bondage.
Kind of seems like celebrating the feasts would be the door one would enter in order to be entangled again in the Yoke of Bondage.
I do think Christians could receive blessing and knowledge from studying the feasts and understanding that they are Blessings we receive in Christ. However, they must be careful of the temptation of seeming to be "holier" or "more special" because they think they are following Gods Way. There is no way for us to be more Holy or more Righteous than we are in Christ.
1 Corinthians 1:29-31
29 That no flesh should glory in his presence.
30 But of him are ye in Christ Jesus, who of God is made unto us wisdom, and righteousness, and sanctification, and redemption:
31 That, according as it is written, He that glorieth, let him glory in the Lord.