Hypersonic cruise missiles and HGVs are current trends to bypass defenses. However as we all know we need quiet some time like a decade to develop such systems. Anti ship ballistic missiles are used by several countries and they have about 1500-2000 km range and they manuever to bypass ship abms. Maneuvering ballistic missiles are also an option like iskandar or similar systems. Mirv can also be effective. They need to put S400 close to your borders to take out your bms in boost phase which makes S400 vulnurable to be detected by drones,sar-optical-satellites,elint etc. and swarm attacked.
Another option is I think staying at the high supersonic range. That is using supersonic cruise missiles but with some improvements like reducing rcs. There is already developed technology from cold war decades ago which we can improve with some tweaks and using modern electronics so they can be effective today.
For example the D-21 spy drone has a small size and looks very sleek and stealthy. It has mach 3-3.5 speed with a ramjet engine and about 5000km range. It has obvious resembelence to SR-71 and stealth was a consideration that was used on the design of SR-71 which was a spy plane as well.
The concept would have given the service a penetrating high-speed strike asset, something it is still interested in to this day.
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It was considered as a cruise missile later on but complicated air launch , carrying it over SR-71 and for similar reasons it was discarded or maybe it was not discarded and developed secretly later on.
I think it still has cruise missile potential with some stealth, high speed and long range combination. It can be used for anti shipping as well as ground attack. A scaled down variant of this can be ground launched by rockets to high altitude(about 20km) and gain sufficient speed for ramjet to activate in my opinion with sufficient ranges like 1000-2000km or more.
Ground launch of ramjet cruise missile by rocket assist example is below. It is an intercontinental cruise missile and scale is much higher ofcourse like a space shuttle. A miniature variant of this and with current long range drone technology plus a radar seeker on its nose for anti-shipping it can be used to bypass defenses in my opinion.
Later on we can integrate long range hcms and hgvs but during that period these can be developed-integrated in a much shorter time.