The VAT returns are supposed to be replaced by a new SAF-T structure (SAFT_VDEK). This new structure will combine data from the VAT Return and the current periodic SAF-T for VAT. Based on the press, the plan of the Polish Ministry of Finance is to implement the SAFT_VDEK structure from January 2019 and to abolish the VAT returns as from July 2019. So during the first six months of 2019, businesses will submit both SAFT_VDEK and VAT returns.
Please note however that the Ministry has not yet published a draft of the regulation that would implement such changes nor details on the structure of the new SAFT structure.