I think the communion recipients will either be advised to bow reverently to the Priest or Deacon, or simply kneel on the floor. A lot of Catholics bow their heads slightly already, in churches without rails.
Of course, Episcopal churches generally never got rid of the altar rails, and I had always knelt to receive Communion (except a Mass in a gymnasium) before I joined the Catholic Church.
Putting a rail into our sanctuary would be easy - even though it's a new church and has never had a rail before. There are 2 or 3 steps up to the altar from the floor of the nave, and it would be a fairly simply matter to bolt the rail to the edge of the altar level and put moveable kneeling cushions on the top step.
Bowing is part of veneration when recieving. The majority of communicants do not bow, genuflect or show any adoration at all. The best thing would be to kneel. Then there will, finally, be some holiness shown.
I always understood that we were bowing our heads to the Holy Eucharist — Jesus Christ. Not the priest or deacon.