Transport for London take over responsibility for the Heathrow Connect Service on 20th May.
This will have no immediate impact on frequency of service. There will continue to be two trains an hour between Paddington and Heathrow, stopping at West Ealing station on the way. TfL will initially be using the Heathrow Connect trains although they may be rebadged with the TfL roundel.
From 21st May, TfL will also take over the existing half hourly service between Paddington and Hayes & Harlington. On this service they will introduce new trains so this will be the first time that people using the line into Paddington will have a chance to try the trains which will be used on the Elizabeth line. At some time later in the year, TfL is also planning to start to replace the old Heathrow Connect trains into Heathrow with the new trains.
Essentially there will be no significant difference to services from May; it will just be that some will be run by TfL rather than GWR or Heathrow Connect. However, there will be one immediate benefit for those using the trains to Heathrow which is that customers will be able to use Oyster cards and other contactless cards to pay for the journey. They are also likely to find that the cost of the journey is in most cases slightly less than at present if they use contactless payments. In addition, zone 1-6 travelcards, passes and other concessions are likely to be valid on the journey between Hayes & Harlington and Heathrow, as well as between Paddington and Hayes & Harlington, whereas they cannot be used at present on the Heathrow link.
In terms of the new station, Network Rail is currently procuring a new contractor to carry out the main building works at West Ealing. Please find here a link to the plans for the station which have been approved by the council. The contractor will be appointed in the summer and start work on site soon after. Network Rail is not yet able to provide a detailed programme for the work but expects that the station will be open in advance of the full Elizabeth line services starting in December 2019. December 2019 will be the first time that passengers will be able to get on a train at West Ealing and travel into the Elizabeth line tunnels under central London through Paddington to Bond Street, Tottenham Court Road, Liverpool Street and beyond without needing to change train.