New ticket office opened at Hammersmith H&C

What is the process required to safeguard a route? Although I can't see this as a viable project at this stage, I agree it is still important to keep options open for future extensions.

In terms of a link, and assuming these building all came up for redevelopment (unlikely), the old LSWR viaduct rises between the eastbound Piccadilly and District tracks. Therefore you'd have to rebuild the alignment. And then you'd have the operational challenge of dovetailing the H&C into the District line.

Interesting idea though...

As I understand it,a route is safeguarded by the local planning authority (in this case Hammersmith and Fulham Council) though they might be directed to do so by a higher authority in Central Government.
The planning authority should produce a develpment plan for its area,and this would make it much harder to get planning permission for a development which contradicts the plan.
If H&F decided (or was told) this route might be a good idea,it would find its way onto the development plan.
To give a frinstance,a friend who lives in Chenies St (near Goodge St station) got a letter from Camden Council informing of a new development in her street,and giving notice for any objections etc.
The letter also said that the foundation depth was limited in order to safeguard the Chelsea-Hackney line route.

As I understand it....The Department of Transport would probably have a hand in it,as would the Minister ultimately responsible for planning (Home Secretary? Environment Minister?) TfL would certainly be involved,probably as promoter of such a scheme.
If they all agreed it should be done,the Minister could direct H&F to put it in their development plan.
(This I do know) If H&F decided unilaterally to put it in its development plan,and someone wanted to build on the route without the burden of having to keep the route clear they would first exhaust the Council's own planning appeals procedure,then they would appeal to the Minister who would (in this particular scenario) rule in favour of the developer as the safeguarding wasn't his own idea or from DfT or TfL who are the only people with the money to realise such a scheme.
Look how difficult it is to build the Croxley Link when all these bodies appear to be not against (but not wildly enthusiastic either) and there is no developer crying "Foul!"
I personally think it is a great idea,but,because it by-passes BOTH Hammersmith stations,it will need a new one of its own (Grove Rd) so it will be so expensive it would be very difficult to get built.....

Ultimately,the Minister responsible for planning (used to be the Environment Minister but so much gets changed so frequently) has the final say.
A developer who wants to contradict a local authority's development plan can appeal to the Minister,and the appeal may be successful.
Or,conversely,the Minister can "call in" a scheme,effectively taking the decision out of the local authority's hands,if he believes the decision is of "strategic" value....though this is usually used to get big schemes built against purely local opposition.
Local authorities can push schemes through off their own bat,but like everything in life,the more pepole you have "on side" (and the more powerful those people are) the more likely it is to succeed.
The schemes most likely to succeed are ones adopted by the Department for Transport (who also have a remit for strategic planning,though,frankly,rail is pretty low on their priorities),but even these have to be approved by the minister responsible for planning....however,as this is "politics" a quiet word would be had before submitting such a scheme so only schemes certain to be approved would be submitted....