At least six games are to be played in Cardiff during the tournament, and with the turf currently being replaced several times a year, the WRU believes using a synthetic surface could be a practical alternative.
"(An artificial grass pitch) is being given serious consideration. We are looking at the implications," Lewis said in an interview with The Sunday Times.
A layer of stone, a thick black rubber shock pad and a covering of artificial green yarn 5cm deep with an in-fill of black rubber crumb make up the surface, which has been approved by the International Rugby Board.
The only concern the WRU has is whether the pitch will be able to take hosting music shows, which regularly occur at the stadium.
"They use some very serious trucks for their equipment," Lewis said. "We'd need to be satisfied that the new surface can take it."