I think that there will never be unity between the sects and the Catholic Church. Just as I do not believe they will ever unite with the main Protestant groups.
Already there is a lot of cooperation between Anglicans Methodists, Catholics etc. But the SDA and JW’s seem further away than ever.
I think it is not desirable that we ‘all become one’. I see God as a great mountain. Wherever you stand, you see a different picture. On the north side, pine trees and snow, on the south short grass, luscious plants and citrus fruit, on the east and west somewehere in between. So too with Anglican, Methodist, Baptist and Catholic, Unitarian, Society of Friends.
In nature, it seems that God is about diversity. So too human culture. We can work together and have joint worship such as the Easter Witness which is often very ecumenical.
In one community, up until recently the local Methodist Minister was our own Deacon. He was asked by the Methodist community to undertake a caretaker role following the sudden death of their Minister [an outstanding man of admirable Christian principles and for whom I had a lot of respct].
But, I do not see SDA or JW’s ever being reconciled wiht Methodists or anyone else.