The 144.000 are Jewish people, as the bible says. To admit this would put the GB is trouble.
The only covenant for Christians is the new covenant.
There is no covenant for a kingdom with Christians. There is an assignment that Jesus gives to the 12 apostles, who are Jews. In Luke 22:29 the word "covenant" does not appear there.
The wt admits there is no word covenant there.If you have NWT with references, look at the apendix, pages 1584-1585 7D “Covenant” , it is an apendix for the word covenant and there are listed all the verses where "covenant" appears, Luke 22:29 is not among them.
So the NWT with References appendix is proof they mistranslated Luke 22:29 and inserted a covenant for the kingdom with the disciples.
It is not like the kingdom is taken from the Jews and given to Christians, but rather the new covenant allows people from other nations who become Christians to co-inherit the kingdom with Jews. It is an extension, not a replacement.
The number in revelations refers to Jewish people who will have a special place in God's kingdom, not to all anointed.
More about the invented covenant of the wt, a covenant that no one else finds in the bible, but the greedy GB of WT:
http://perimeno.ca/Letters_0611_covenant-for-a-kingdom.htm
Look for yourself how other Bibles translate that verse http://biblehub.com/luke/22-29.htm