Managing an Eclectic Layout

I am constantly faced with the quandry of how to proceed with my layout development knowing I don't have a constant theme set in stone. This is particularly frustrating for me in setting the scene on the layout beore even rolling out the various fleets. The problem is I have a love affair with various trains from the late nineteeth and early twentieth centuries through to twenty first century high speed trains. So the theme of the layout needs to accomodate a 4-6-2 steam hauled heavy weight passenger service from the pre-1920's Europe and Australia through to the modernist Eurostar and TGV's ... without winding up looking ridiculous.

Whilst my love affair harks back to the romance of the rails being founded in passenger traffic,my vision isn't void of freight traffic and yarding activities. However, passenger focus remains the prime driving force behind my motivation to establish a layout... So I suppose this is something of a starting point. This still leaves me with a dilema as to the time period of the layout. Too modern and steam traffic will look out of place and too old and the opposite will be true for modern fleet items, which I must admit there really isn't anything too modern in my fleet at this time.

I'd appreciate any comments from any followers how they have dealt with this same issue in the development of their own layouts.