The connection between the Dudding Hill line and the former LNWR line at Harlesden was an afterthought. What is now the bridge over the canal that carries the link was originally the way to a wharf on the canal, going round an impossibly sharp curve on the canal's north bank. The wharf was closed and the bridge dismantled, the latter was subsequently reinstated and the link between the two lines instituted. It may have been one of the various useful connections put in during the Second World War. Prior to this, traffic coming down the LNWR bound for, say, Feltham would have to be reversed at Willesden Junction. The NLS website is currently unavailable; there are 25" and 50" OS maps on it that show the changes.The historic summary of the line given in "St Pancras to St Albans" (Goslin & Connor, Middleton Press, 2002) says that it was built as a connection to the North and South Western Joint Railway at Acton Wells. Another source I have says that the latter railway was constructed as a link between the London and South-Western and the London and North-Western Railways between Willesden and Old Kew junction.
Goslin and Connor go on to say that the Acton Branch was designed by the Midland as a way of connecting to the South of England. In return the L&SWR had running rights to Brent sidings.
So it seems there were no plans for any other branches.
The Midland Railway stations at Dudding Hill & Harlesden both closed to passengers in 1902 (Wikipedia)I was looking the Dudding Hill Line roughly around the closed Harlesden station and was wondering if there were any brief historic ideas for a branch to Willesden Junction towards Euston and onto the West London Line?